Mother is glad that he’s already done_______ 60% of the work in such a short time.(西安市)

A．no less than

B．no more than

C．not more than

D．less than

柴油机冒蓝烟的原因通常是（）。

A.活塞与气缸间隙过大

B.活塞环老化

C.气门间隙过大

D.有水进入