选择句子补全对话。（10分）

A：    1 (      )    . Can you tell me the way to the Children’s Hospital, please?

B：Sure.    2 (      )     and turn right between Book Store and Library.

The white building is the Children’s Hospital.    3 (      )    

A：   4 (      )     . By the way,    5 (      )     .

B：About half an hour.

A：OK. Good-bye.

主风机出口单向阀的作用是防止提升管内油气倒流到主风机内，以防止造成爆炸。