.

It was ___ he came back from Africa that year ___ he met the girl he would like to marry.

A．when; then

B．not; until

C．not until; that

D．only; when

ZD6系列电动转辙机松开摩擦带紧固螺栓，在输出轴不旋转的条件下，测试转辙机空载电流过大的原因之一：两片外齿轮偏心不够（）。

A.45°

B.60°

C.90°

D.180°