基坑采用机械挖土，坑底应保留（）厚基土，用人工清理整平，防止坑底土扰动。

A．100～200mm

B．200～300mm

C．300～400mm

D．400～500mm

根据句意及所给首字母,完成下列句子。

1.The shops were too c    and I didn't enjoy going shopping．

2.The food is very d    .I like it very much.

3.Jim sits in the c    of the classroom.

4.We are very busy. We are studying for the e    .

5.There are a lot of old things on show in the m     ．