We ____ there when it ____ to rain. [ ]

A. were getting-would begin

B. were about to get-began

C. had got-had begun

D. would get-began

当一对啮合齿轮，其中一个主动齿轮由原动机带动旋转，另一从动齿轮与（）相啮合而转动。

A、从动齿轮

B、主动轴

C、主动齿轮

D、从动轴