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Pearls grow inside shellfish （贝类动物）. Shellfish have hard shells. They open and close their shells to catch their food. Their shells are usually grey and ugly on the outside, but shiny and beautiful inside. When something, for example, a little worm or some sand, gets inside a shellfish, the shellfish covers it with layers of mother-of-pearl. After a long time, it becomes a pearl（珍珠）.
A long time ago, people went out to sea in small boats, and dived （潜水）into the water to look for pearls. They worked very quickly because they could not breathe under water. A good diver could work under water for about three minutes. They climbed into the boat again, opened the shells and looked for pearls.
Today many pearls grow in oyster（牡蛎）farms. People buy young oysters and put them in a place called an oyster bed. The oysters eat and grow there. When an oyster is big enough, the farm keeper opens it very carefully. He puts a little bead（珠子）inside its shell. Later the bead becomes a pearl.
Pearls are beautiful and they are always expensive. In the past only rich people could buy pearls. Now pearls are much cheaper because they can be grown on oyster farms. People make things like necklace with them. And some people put pearls on their clothes and shoes, too.
Most pearls are small, hard and round. Most of them are white but some are yellow, green, blue, grey or black. The most expensive pearl is not round. It looks like an egg. It is not very big. It weighs 15.13 grams. It used to be in a king’s crown （王冠）. Someone bought it for US $ 864,280 in 1988.
1. How did people get pearls in the past ?
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2. What is an oyster bed made for?
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3. Why are pearls less expensive now?
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4. How heavy is the most expensive pearl in the world?
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5. Why do people like pearls?
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