We were swimming in the lake suddenly the storm started.A. when B. whileC. untilD. before

问题补充：

We were swimming in the lake suddenly the storm started.

A. when

B. while

C. until

D. before

答案：

(答案→)A. when

B. while

C. until

D. before

解析：考查固定句型。固定句型:be doing sth when…正在做某事在这时…when后面的句子指发生了意料之外的事情。When是一个并列连词，意为“在这时”。句意：我们正在湖里游泳，在这时突然下起了大暴雨。故A正确。