________ tomorrow, I would take a bus to school.

A．If it rains

B．If it was to rain

C．Should it rain

D．Rained it

（）联轴器结构简单，维修保养方便，能缓和冲击和振动，延长传动装置零件的使用寿命。

A.弹性

B.简易

C.凸缘

D.凸台