英語專業(yè)四級聽力周計劃：模擬真題12

About 40% of the different kinds of sharks lay eggs.

The others give birth to live young.

Some sharks carry their young inside their bodies like humans do.

Scientists are beginning to understand the importance of sharks to humans.

Medical researchers want to learn more about the shark's body defense system against diseases.

They know that sharks recover quickly from injuries.

Sharks appear never to suffer infections, cancer or heart disease.