--- What on earth are the police busy with?
--- They have been investigating how the train crash .
A. came out
B. came across
C. came about
D. came up
网友回答
A. came out
B. came across
(答案→)C. came about
D. came up
解析：句意为：----警察们究竟在忙什么呢？ ---他们正在调查这次火车相撞的原因（是怎么发生的）. e out 出版，发行，发现； e across偶然遇到，碰到；e about 发生，产生；e up 想出，提出。故答案应为C。