——Mr Smith looks rather a kind man.

——But in fact he is cold and hard on us. You ____ believe it!

A．shouldn't

B．wouldn't

C．mustn't

D．needn't

数控车床主轴采用前端定位，后端浮动的结构是为了（）。

A、便于调正精度

B、便于调整间隙

C、便于装配与调正

D、防止受热伸长