On a hot day，many people like to go to the beach.Some beaches，however，are not safe for swimming.

At some beaches，there are sharks in the water.So people put out shark nets.They help stop too many sharks from getting close to the beach.Sharks can still swim under or around the net.But if they try to swim through，they will get caught.Sharks can die if they are not cut free.

    Shark nets don't just catch sharks.They can catch other animals，too.They have caught dolphins，stingrays and turtles.Even a whale has been caught in a shark net.I took many people to get it free.

    Some animals are not so lucky.They are killed in the nets.One day，a whale was swimming with her calf.The calf got caught in a shark net.The mother whale tried to get the calf to come with her.The calf was caught in the net.It couldn't get free.The mother had to watch it die.

    Many people think shark nets should not be used.Sharks are important to the ocean.They eat sick and dead fish.They help to keep the ocean clean.Sharks are the lions and the tigers of the sea.

    Some people think there are other ways to keep beach safe for people.Sharks potters are people who watch for sharks.They go to a high place.Then they can look down on the beach.If they see a shark，a siren（汽笛）will sound.They put up a white flag.Then people get out of the water.

    After all，the water is a shark's home.

（1）What can we know about shark nets according to the passage？ 　　

A.They are used to keep sharks from coming near the beach.

B.People place them to catch sharks，dolphins，stingrays and turtles.

C.Sharks will be caught when they get close to them.

D.All the animals caught by them are set free.

（2）What does the underlined word "calf" mean in paragraph 4？ 　 　

A.A huge whale.

B.A young whale.

C.A father whale.

D.A mother whale.

（3）What does the writer imply（暗示）about the beach safety？ 　　

A.People should keep away from beaches.

B.Everyone should work as a shark spotter.

C.It's not the best way to put out shark nets.

D.Some dangerous beaches should be shut down.