Uncle Wang is_____ the barber’s at the moment, so you have to talk to him _____ the phone.

A．in; in

B．at; on

C．on; at

D．at; at

（）有内圈外圈滚动体和保持架组成。

A.滑动轴承

B.滚动轴承

C.向心轴承

D.推力轴承