We had hardly arrived at the foot of the Yuntai Mountain it began to rain heavily .A. than

问题补充：

We had hardly arrived at the foot of the Yuntai Mountain it began to rain heavily .

A. than

B. when

C. until

D. after

答案：

A. than

(答案→)B. when

C. until

D. after

解析：句意：我们差不多到达云台山脚下了，突然天开始下起了大雨。此处when意为：突然。故选B。