On a rainy day I was riding my bike to pick up my son a terrible accident happened ahead.
A. who
B. which
C. while
D. when
网友回答
A. who
B. which
C. while
(答案→)D. when
解析:考查固定句式。固定句式:be doing sth when…正在做某事,在这时发生了意料之外的事情。句意:在一个雨天,我正在骑车接我的儿子在这时前面一起可怕的事故发生了。故D项正确。