Today ,more and more sharks（鲨鱼）die because of humans' activities .Sharks are facing hard living conditions these days. As we know, sharks are among the oldest animals on earth. There are over 500 kinds of sharks living in the oceans. Most of them are quite large and they are about two meters long. Yet some are small, for example, the dogfish shark is less than 20cm long. The shark has a strong sense of smell. This sense helps sharks find their food. Sharks eat fish and plants in the ocean.
Sharks grow slowly. About forty percent of all sharks lay（产） eggs. The others give birth to baby sharks. Some sharks carry their babies inside their bodies as humans do. Some sharks are not able to have babies until they are twenty years old. And each of them gives birth to at most ten baby sharks.
People kill sharks for food, medicine and their skin（皮肤）. Experts say the market needs much more sharks. In Asia, people enjoy a kind of food made from shark fins（鱼翅）.
For the reasons above, some sharks are endangered.
