Sharks have lived in the world's oceans for millions of years. A shark has an extremely good sense of smell. It can find small amounts of substances in the water, such as blood, body liquids and chemicals produced by animals. These powerful senses help them find their food.    
Sharks grow slowly. About forty percent of the different kinds of sharks lay eggs.    Some sharks carry their young inside their bodies as humans do. Some sharks are not able to reproduce until they are twenty years old. Most reproduce only every two years. And they give birth to fewer than ten young sharks. For this reason, over-fishing of sharks is of special danger to the future of the animal.
  .They eat injured and diseased fish. Their hunting activities mean that the numbers of other fish in the ocean do not become too great. This protects the plants and other forms of life that exist in the oceans.
People hunt sharks for sport, food, medicine and their skin. Experts say the international market for some kinds of sharks has increased greatly because many parts of a shark are valuable.   . Shark liver oil is a popular source of Vitamin. The skin of a shark can be used like leather. In Asia, people enjoy a kind of soup made from shark fins. Experts say a fisherman can earn a lot of money for even one kilogram of shark fins.
Sharks are among the oldest animals on Earth.     If too many sharks in one area are killed, the group of shark may never return to normal population levels

A．The others give birth to live young.

B．Sharks are important for the health of the world's oceans.

C．This is a threat to other form of life in the ocean.

D．Collectors pay thousands of dollars for the jaws of a shark.

E. Sharks are valuable to us and we can make full use of them.
F. But some sharks are in danger of disappearing from Earth.
G. Sharks eat fish, other sharks, and plants that live in the ocean