—What a smart and hard-working boy he is!

—Right. ________ a possibility that he will win the first place in the competition.

A．This is

B．It remains

C．There seems

D．That appears

轴上零件常用的固定方式有（）。

A.套筒

B.圆螺母

C.轴端挡圈

D.法兰