阅读理解。阅读下列内容，从每小题所给的A、B、C、D四个选项中选出一个最佳答案。

If visitors cannot see the animals, the animals may be______.

A．playing

B．eating

C．acting

D．sleeping

Jack is eight years old. He goes to the zoo with his 58-year-old grandfather．How much should they pay for visiting the zoo?

A．$18.

B．$22.

C．$28.

D．$32.

What should we do in order not to frighten the animals?

A．We should ride bikes.

B．We should keep quiet.

C．Ｗe should feed the animals.

D．We should keep the zoo clean.