Read the passage carefully and choose the correct answer.

Natural beauty of Maldives

Maldives is known as “the tropical paradise” for reasons. Its beauty is none like other. Maldives is a tropical country with separated islands, which are separated by sea. Each island is surrounded by stunning white sandy beaches. It is a wonderful experience to visit and explore the beauty of the islands.  

The sea covers about 99% of the Maldives and it is where most attractive things lie in. There are over five thousand coral reefs and plenty of reef fish, corals, marine mammals, and so many other marine lives. And that is the reason people say, diving in Maldives is unforgettable.

Almost all the islands in Maldives are surrounded by beautiful pure white sandy beaches. Even if you have nothing else to do, I am sure you won't get bored walking in the soft white sandy beaches and leaving your foot prints on.

When you look at an island from a distance, you can find green trees before anything else, and specially the coconut palms. That brings more beauty to the islands, plus you get amazing drink out of the coconut palms.

Traveling in a sea plane and watching the beautiful islands from the window is the most wonderful experience you could ever have. Islands are formed in way that makes a round which is called as an atoll. When you see them from sea plane view, it will look like a chain of pearls.

With the natural and beautiful surrounding, you could have a memorable trip in Maldives. It is also an ideal place to have a family holiday, where you can spend lovely moments with fun and enjoyment in the beautiful pure white beaches.

(https://www.maldives.com/natural-beauty-surrounding-maldives/)

According to the passage, what is an atoll?