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Patient zero is generally taken to mean the first case in a disease outbreak – but the term is often applied in different ways. When it comes to zoonotic diseases (ones that jump from animals to humans, like SARS-CoV-2), patient zero might refer to the first-ever human case – the point at which the virus spills over from an animal to a human. For the general public, however, patient zero is often used to refer to the first case in a particular region, or the first case that's come to the attention of health authorities. However, these are not always the same thing. Sometimes the first case that's notified to us is not the first case in an outbreak. Similarly, just because someone is identified as the first case doesn't mean they spread the disease to anyone else, or behaved irresponsibly – with something like coronavirus, they may not even know they're sick.

This is part of the reason why patient zero is not a term epidemiologists or public health experts tend to use - it's not specific enough. They prefer the term index case to refer to the first person officials became aware of in an outbreak (which gives them a clue something's going on), and primary case to refer to the person who introduces a disease into a new population - a community, country or the world. Sometimes, the primary case and the index case will be the same person, but not always. For many outbreaks - such as HIV/AIDS, and possibly COVID-19 – we will never know the primary case.

While the use of the term patient zero can be fraught, tracing outbreaks back to their beginnings remains important in public health. In the early days of an outbreak, it's still possible to catch embers of disease before they become full-blown fires. "You can actually stamp them out, by identifying every case, tracking every contact, quarantining them, making sure there's no further spread," Professor Raina Macintyre, head of biosecurity at UNSW's Kirby Institute says. But even after those critical first days or weeks, tracing cases back to patient zero can still give both health experts and relevant authorities for insights into how disease spreads and understands the role that health services and adequate sanitation systems play in controlling the spread of the disease. That's the purpose of trying to understand an index case or a first case – to establish the opportunity to learn from the breakout and try to make sure it doesn't happen again.

What might serve as the best title for the whole reading passage?

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Antioxidants are substances - artificial or natural - that prevent and slow cell and tissue damage by attacking free radicals, which are molecules that have an unpaired electron. Free radicals are natural byproducts of our metabolism and are also generated in response to environmental stressors, such as exposure to pollution, X-rays or cigarette smoke. In high quantities, free radicals can cause oxidative stress, which is when the body has too many free radicals that start to destroy DNA, fatty tissue and proteins. [A]

Unlike free radicals, antioxidants have extra electrons. This means that they can pass their surplus electrons to free radicals, stabilizing the free radicals so they can no longer damage the body's cells and tissues. In doing so, antioxidants ward off or slow oxidative stress, preventing serious illnesses. Oxidative stress has been linked with illnesses such as cancer, heart disease and some neurodegenerative diseases, including Alzheimer's and Parkinson's disease. The best way to increase antioxidants in the body and maintain a healthy balance of free radicals is to incorporate antioxidant-rich foods into your diet. [B]

The term “antioxidant” is often used to describe different foods, but it more accurately describes chemical property. Any substance that can strip free radicals of their damaging properties is considered an antioxidant. Researchers have discovered hundreds of substances that fit the antioxidant description, and there are perhaps thousands more. Vitamin C and vitamin E are two of the most common antioxidants found in food. In addition to fighting free radicals, vitamin C supports the immune system and helps repair bones, teeth and cartilage. Vitamin E is a powerful tool in maintaining eye health, producing hormones that regulate blood pressure and repairing muscles after exercise. Carotenoids- a class of compounds found in fruits and vegetables that are red, orange and yellow - are also well-known antioxidants.

Antioxidant carotenoids include beta-carotene, lycopene, lutein and zeaxanthin. However, taking high doses of some carotenoid supplements, such as beta-carotene. Can increase health risks, such as an increased chance of lung cancer in smokers. [C]

Antioxidants are most often in fruits, vegetables and legumes, although they can be found in almost every food group. Fruits contains essential nutrients such as potassium, fibre and folate - nutrients that help maintain blood pressure, lower cholesterol and repair body tissues. Blueberries, cranberries, apples, strawberries and more are all filled with antioxidants. Dried fruits - although often high in processed sugars - have a higher antioxidant ratio than fresh fruits, since they lose mass from water. They act as quick antioxidant fuel due to their high concentration of antioxidants. Carotenoids are found in red, orange or yellow vegetables. Many green vegetables such as kale, broccoli and spinach are excellent sources of antioxidants, namely quercetin and lutein. [D]

The word "fit" is closest in meaning to________.

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Antioxidants are substances - artificial or natural - that prevent and slow cell and tissue damage by attacking free radicals, which are molecules that have an unpaired electron. Free radicals are natural byproducts of our metabolism and are also generated in response to environmental stressors, such as exposure to pollution, X-rays or cigarette smoke. In high quantities, free radicals can cause oxidative stress, which is when the body has too many free radicals that start to destroy DNA, fatty tissue and proteins. [A]

Unlike free radicals, antioxidants have extra electrons. This means that they can pass their surplus electrons to free radicals, stabilizing the free radicals so they can no longer damage the body's cells and tissues. In doing so, antioxidants ward off or slow oxidative stress, preventing serious illnesses. Oxidative stress has been linked with illnesses such as cancer, heart disease and some neurodegenerative diseases, including Alzheimer's and Parkinson's disease. The best way to increase antioxidants in the body and maintain a healthy balance of free radicals is to incorporate antioxidant-rich foods into your diet. [B]

The term “antioxidant” is often used to describe different foods, but it more accurately describes chemical property. Any substance that can strip free radicals of their damaging properties is considered an antioxidant. Researchers have discovered hundreds of substances that fit the antioxidant description, and there are perhaps thousands more. Vitamin C and vitamin E are two of the most common antioxidants found in food. In addition to fighting free radicals, vitamin C supports the immune system and helps repair bones, teeth and cartilage. Vitamin E is a powerful tool in maintaining eye health, producing hormones that regulate blood pressure and repairing muscles after exercise. Carotenoids- a class of compounds found in fruits and vegetables that are red, orange and yellow - are also well-known antioxidants.

Antioxidant carotenoids include beta-carotene, lycopene, lutein and zeaxanthin. However, taking high doses of some carotenoid supplements, such as beta-carotene. Can increase health risks, such as an increased chance of lung cancer in smokers. [C]

Antioxidants are most often in fruits, vegetables and legumes, although they can be found in almost every food group. Fruits contains essential nutrients such as potassium, fibre and folate - nutrients that help maintain blood pressure, lower cholesterol and repair body tissues. Blueberries, cranberries, apples, strawberries and more are all filled with antioxidants. Dried fruits - although often high in processed sugars - have a higher antioxidant ratio than fresh fruits, since they lose mass from water. They act as quick antioxidant fuel due to their high concentration of antioxidants. Carotenoids are found in red, orange or yellow vegetables. Many green vegetables such as kale, broccoli and spinach are excellent sources of antioxidants, namely quercetin and lutein. [D]

According to the passage, which antioxidant is especially good for people who do a lot of physically demanding activities?

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Antioxidants are substances - artificial or natural - that prevent and slow cell and tissue damage by attacking free radicals, which are molecules that have an unpaired electron. Free radicals are natural byproducts of our metabolism and are also generated in response to environmental stressors, such as exposure to pollution, X-rays or cigarette smoke. In high quantities, free radicals can cause oxidative stress, which is when the body has too many free radicals that start to destroy DNA, fatty tissue and proteins. [A]

Unlike free radicals, antioxidants have extra electrons. This means that they can pass their surplus electrons to free radicals, stabilizing the free radicals so they can no longer damage the body's cells and tissues. In doing so, antioxidants ward off or slow oxidative stress, preventing serious illnesses. Oxidative stress has been linked with illnesses such as cancer, heart disease and some neurodegenerative diseases, including Alzheimer's and Parkinson's disease. The best way to increase antioxidants in the body and maintain a healthy balance of free radicals is to incorporate antioxidant-rich foods into your diet. [B]

The term “antioxidant” is often used to describe different foods, but it more accurately describes chemical property. Any substance that can strip free radicals of their damaging properties is considered an antioxidant. Researchers have discovered hundreds of substances that fit the antioxidant description, and there are perhaps thousands more. Vitamin C and vitamin E are two of the most common antioxidants found in food. In addition to fighting free radicals, vitamin C supports the immune system and helps repair bones, teeth and cartilage. Vitamin E is a powerful tool in maintaining eye health, producing hormones that regulate blood pressure and repairing muscles after exercise. Carotenoids- a class of compounds found in fruits and vegetables that are red, orange and yellow - are also well-known antioxidants.

Antioxidant carotenoids include beta-carotene, lycopene, lutein and zeaxanthin. However, taking high doses of some carotenoid supplements, such as beta-carotene. Can increase health risks, such as an increased chance of lung cancer in smokers. [C]

Antioxidants are most often in fruits, vegetables and legumes, although they can be found in almost every food group. Fruits contains essential nutrients such as potassium, fibre and folate - nutrients that help maintain blood pressure, lower cholesterol and repair body tissues. Blueberries, cranberries, apples, strawberries and more are all filled with antioxidants. Dried fruits - although often high in processed sugars - have a higher antioxidant ratio than fresh fruits, since they lose mass from water. They act as quick antioxidant fuel due to their high concentration of antioxidants. Carotenoids are found in red, orange or yellow vegetables. Many green vegetables such as kale, broccoli and spinach are excellent sources of antioxidants, namely quercetin and lutein. [D]

Which serve as the best title for the last paragraph?

Read the message and choose the best answer.

Antioxidants are substances - artificial or natural - that prevent and slow cell and tissue damage by attacking free radicals, which are molecules that have an unpaired electron. Free radicals are natural byproducts of our metabolism and are also generated in response to environmental stressors, such as exposure to pollution, X-rays or cigarette smoke. In high quantities, free radicals can cause oxidative stress, which is when the body has too many free radicals that start to destroy DNA, fatty tissue and proteins. [A]

Unlike free radicals, antioxidants have extra electrons. This means that they can pass their surplus electrons to free radicals, stabilizing the free radicals so they can no longer damage the body's cells and tissues. In doing so, antioxidants ward off or slow oxidative stress, preventing serious illnesses. Oxidative stress has been linked with illnesses such as cancer, heart disease and some neurodegenerative diseases, including Alzheimer's and Parkinson's disease. The best way to increase antioxidants in the body and maintain a healthy balance of free radicals is to incorporate antioxidant-rich foods into your diet. [B]

The term “antioxidant” is often used to describe different foods, but it more accurately describes chemical property. Any substance that can strip free radicals of their damaging properties is considered an antioxidant. Researchers have discovered hundreds of substances that fit the antioxidant description, and there are perhaps thousands more. Vitamin C and vitamin E are two of the most common antioxidants found in food. In addition to fighting free radicals, vitamin C supports the immune system and helps repair bones, teeth and cartilage. Vitamin E is a powerful tool in maintaining eye health, producing hormones that regulate blood pressure and repairing muscles after exercise. Carotenoids- a class of compounds found in fruits and vegetables that are red, orange and yellow - are also well-known antioxidants.

Antioxidant carotenoids include beta-carotene, lycopene, lutein and zeaxanthin. However, taking high doses of some carotenoid supplements, such as beta-carotene. Can increase health risks, such as an increased chance of lung cancer in smokers. [C]

Antioxidants are most often in fruits, vegetables and legumes, although they can be found in almost every food group. Fruits contains essential nutrients such as potassium, fibre and folate - nutrients that help maintain blood pressure, lower cholesterol and repair body tissues. Blueberries, cranberries, apples, strawberries and more are all filled with antioxidants. Dried fruits - although often high in processed sugars - have a higher antioxidant ratio than fresh fruits, since they lose mass from water. They act as quick antioxidant fuel due to their high concentration of antioxidants. Carotenoids are found in red, orange or yellow vegetables. Many green vegetables such as kale, broccoli and spinach are excellent sources of antioxidants, namely quercetin and lutein. [D]

The sentence "This is where antioxidants can save the day." can best fit which of the numbered spaces in the passage.

Read the message and choose the best answer.

Antioxidants are substances - artificial or natural - that prevent and slow cell and tissue damage by attacking free radicals, which are molecules that have an unpaired electron. Free radicals are natural byproducts of our metabolism and are also generated in response to environmental stressors, such as exposure to pollution, X-rays or cigarette smoke. In high quantities, free radicals can cause oxidative stress, which is when the body has too many free radicals that start to destroy DNA, fatty tissue and proteins. [A]

Unlike free radicals, antioxidants have extra electrons. This means that they can pass their surplus electrons to free radicals, stabilizing the free radicals so they can no longer damage the body's cells and tissues. In doing so, antioxidants ward off or slow oxidative stress, preventing serious illnesses. Oxidative stress has been linked with illnesses such as cancer, heart disease and some neurodegenerative diseases, including Alzheimer's and Parkinson's disease. The best way to increase antioxidants in the body and maintain a healthy balance of free radicals is to incorporate antioxidant-rich foods into your diet. [B]

The term “antioxidant” is often used to describe different foods, but it more accurately describes chemical property. Any substance that can strip free radicals of their damaging properties is considered an antioxidant. Researchers have discovered hundreds of substances that fit the antioxidant description, and there are perhaps thousands more. Vitamin C and vitamin E are two of the most common antioxidants found in food. In addition to fighting free radicals, vitamin C supports the immune system and helps repair bones, teeth and cartilage. Vitamin E is a powerful tool in maintaining eye health, producing hormones that regulate blood pressure and repairing muscles after exercise. Carotenoids- a class of compounds found in fruits and vegetables that are red, orange and yellow - are also well-known antioxidants.

Antioxidant carotenoids include beta-carotene, lycopene, lutein and zeaxanthin. However, taking high doses of some carotenoid supplements, such as beta-carotene. Can increase health risks, such as an increased chance of lung cancer in smokers. [C]

Antioxidants are most often in fruits, vegetables and legumes, although they can be found in almost every food group. Fruits contains essential nutrients such as potassium, fibre and folate - nutrients that help maintain blood pressure, lower cholesterol and repair body tissues. Blueberries, cranberries, apples, strawberries and more are all filled with antioxidants. Dried fruits - although often high in processed sugars - have a higher antioxidant ratio than fresh fruits, since they lose mass from water. They act as quick antioxidant fuel due to their high concentration of antioxidants. Carotenoids are found in red, orange or yellow vegetables. Many green vegetables such as kale, broccoli and spinach are excellent sources of antioxidants, namely quercetin and lutein. [D]

Who do you think the article is most likely written for?

Read the message and choose the best answer.

Antioxidants are substances - artificial or natural - that prevent and slow cell and tissue damage by attacking free radicals, which are molecules that have an unpaired electron. Free radicals are natural byproducts of our metabolism and are also generated in response to environmental stressors, such as exposure to pollution, X-rays or cigarette smoke. In high quantities, free radicals can cause oxidative stress, which is when the body has too many free radicals that start to destroy DNA, fatty tissue and proteins. [A]

Unlike free radicals, antioxidants have extra electrons. This means that they can pass their surplus electrons to free radicals, stabilizing the free radicals so they can no longer damage the body's cells and tissues. In doing so, antioxidants ward off or slow oxidative stress, preventing serious illnesses. Oxidative stress has been linked with illnesses such as cancer, heart disease and some neurodegenerative diseases, including Alzheimer's and Parkinson's disease. The best way to increase antioxidants in the body and maintain a healthy balance of free radicals is to incorporate antioxidant-rich foods into your diet. [B]

The term “antioxidant” is often used to describe different foods, but it more accurately describes chemical property. Any substance that can strip free radicals of their damaging properties is considered an antioxidant. Researchers have discovered hundreds of substances that fit the antioxidant description, and there are perhaps thousands more. Vitamin C and vitamin E are two of the most common antioxidants found in food. In addition to fighting free radicals, vitamin C supports the immune system and helps repair bones, teeth and cartilage. Vitamin E is a powerful tool in maintaining eye health, producing hormones that regulate blood pressure and repairing muscles after exercise. Carotenoids- a class of compounds found in fruits and vegetables that are red, orange and yellow - are also well-known antioxidants.

Antioxidant carotenoids include beta-carotene, lycopene, lutein and zeaxanthin. However, taking high doses of some carotenoid supplements, such as beta-carotene. Can increase health risks, such as an increased chance of lung cancer in smokers. [C]

Antioxidants are most often in fruits, vegetables and legumes, although they can be found in almost every food group. Fruits contains essential nutrients such as potassium, fibre and folate - nutrients that help maintain blood pressure, lower cholesterol and repair body tissues. Blueberries, cranberries, apples, strawberries and more are all filled with antioxidants. Dried fruits - although often high in processed sugars - have a higher antioxidant ratio than fresh fruits, since they lose mass from water. They act as quick antioxidant fuel due to their high concentration of antioxidants. Carotenoids are found in red, orange or yellow vegetables. Many green vegetables such as kale, broccoli and spinach are excellent sources of antioxidants, namely quercetin and lutein. [D]

According to the passage, which of the following is true about free radicals?

Read the message and choose the best answer.

Antioxidants are substances - artificial or natural - that prevent and slow cell and tissue damage by attacking free radicals, which are molecules that have an unpaired electron. Free radicals are natural byproducts of our metabolism and are also generated in response to environmental stressors, such as exposure to pollution, X-rays or cigarette smoke. In high quantities, free radicals can cause oxidative stress, which is when the body has too many free radicals that start to destroy DNA, fatty tissue and proteins. [A]

Unlike free radicals, antioxidants have extra electrons. This means that they can pass their surplus electrons to free radicals, stabilizing the free radicals so they can no longer damage the body's cells and tissues. In doing so, antioxidants ward off or slow oxidative stress, preventing serious illnesses. Oxidative stress has been linked with illnesses such as cancer, heart disease and some neurodegenerative diseases, including Alzheimer's and Parkinson's disease. The best way to increase antioxidants in the body and maintain a healthy balance of free radicals is to incorporate antioxidant-rich foods into your diet. [B]

The term “antioxidant” is often used to describe different foods, but it more accurately describes chemical property. Any substance that can strip free radicals of their damaging properties is considered an antioxidant. Researchers have discovered hundreds of substances that fit the antioxidant description, and there are perhaps thousands more. Vitamin C and vitamin E are two of the most common antioxidants found in food. In addition to fighting free radicals, vitamin C supports the immune system and helps repair bones, teeth and cartilage. Vitamin E is a powerful tool in maintaining eye health, producing hormones that regulate blood pressure and repairing muscles after exercise. Carotenoids- a class of compounds found in fruits and vegetables that are red, orange and yellow - are also well-known antioxidants.

Antioxidant carotenoids include beta-carotene, lycopene, lutein and zeaxanthin. However, taking high doses of some carotenoid supplements, such as beta-carotene. Can increase health risks, such as an increased chance of lung cancer in smokers. [C]

Antioxidants are most often in fruits, vegetables and legumes, although they can be found in almost every food group. Fruits contains essential nutrients such as potassium, fibre and folate - nutrients that help maintain blood pressure, lower cholesterol and repair body tissues. Blueberries, cranberries, apples, strawberries and more are all filled with antioxidants. Dried fruits - although often high in processed sugars - have a higher antioxidant ratio than fresh fruits, since they lose mass from water. They act as quick antioxidant fuel due to their high concentration of antioxidants. Carotenoids are found in red, orange or yellow vegetables. Many green vegetables such as kale, broccoli and spinach are excellent sources of antioxidants, namely quercetin and lutein. [D]

How do antioxidants protect the body?