— Do you know       ?

— Sorry, I don’t have a watch.

A． whose watch this is

B． whose watch is this

C． what time it is

D． what time is it

在夹具的实际结构中，支撑点不一定用点或销的顶端，常用（）来代替。

A.点

B.线

C.面

D.圆柱体

E.矩形体

F.圆台