根据答句写出问句。

1、A:                                                           

     B: There are thirty desks in the classroom.

2、A:                                                           

     B: It's about three kilometres away.

3、A:                                                           

     B: He is twenty years old.

4、A:                                                           

     B: The pen is only ten yuan.

5、A:                                                           

     B: It's half past ten.

6、A:                                                           

     B: Twenty plus one is twenty-one.