. Read the passage and answer the following questions: Scientists are now looking for cheaper way to use solar energy to heat air and water. Many buildings are using solar energy to heat their water now. Solar unit on the roofs of buildings collect the energy and use it to heat watwer. Although these units are still very expensive, more and more people are buying solar hot water heaters. Universities and colleges give solar energy courses where students learn to build their own solar collectors. They are also many books that explain the construction of solar collectors. In the future, there will be more and more solar collectors, especially in the sunny desert areas of the world. 23. What are the scientists doing now?  24. Are solar units cheap or expensive?  25. Where do students learn to build their own solar collectors?  26. Do you think solar energy is expensive?  27. Why do(n’t) you think so?  6. Read the passage and answer the following questions: When you have a post-office box, the postman does not bring letters to you, but you go to the post-office and get your letters and parcels from your box. The box is locked, and you have the key, so the letters are quite safe. One day, the headteacher of a school wrote to the post-office and asks for a post-office box for his school. He soon got an answer. It said, “We will give you a post-office box in one month.” Three months later, the headteacher wrote to the post-office again and said, “Why haven’t we got a post-office box yet?” This was how the post-office answered: “ Dear Sir, We gave you a post-office box 2 months ago and wrote to you then to tell you. Here is the key to your box. You will find our letter to you in it” 28. What happens when you have a post-office box? @ 29. Why are letters safe when they are in a post-office box? @ 30. Why did the headmaster write to the post-office? @ 31. Why did he write to the post-office 3 months later? @ 32. When do you think the headmaster will receive the key to his post-box? @ giúp mình với mình cần gấp!