He is believed____________ in at his office on his way home.

A．dropping

B．to have dropped

C．having dropped

D．to be dropped

（）压缩机两主轴承之间，相对两列气缸的曲柄错角为180°，惯性力可完全平衡，转速能提高；相对列的活塞力能互相抵消，减少了主轴颈的受力与磨损。

A、对称平衡式

B、立式

C、角度式

D、对置式