句型转换。

1. It's a white box. (改为复数)

    _________ white _________.

2. He has a short ruler. (改为一般疑问句)

   _________ he _________ a short ruler?

3. His father is fine. (划线部分提问)

   _________ _________ his father?

4. Mary has long legs. (同义句)

   _________ legs _________ long.

5. They're old buses. (改为单数)

   _________ _________ old bus.

学习某材料，10次正好记住，那么学习多少次效果最好呢（）

A.8次

B.10次

C.12次

D.15次

E.20次