---Sam becomes the top student because he is very clever.

---_______. Without the help of his hardworking teachers, he can’t make it at all.

A．I don’t think so.

B．I’m afraid so.

C．I agree with you.

D．I don’t know.

在脚手架上翻脚手板时，应由两人（）按顺序进行。

A.从外向里

B.从里向外

C.从下向上

D.从上向下