What on earth are the police busy with?They have been investigating how the train

问题补充：

--- 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

答案：

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）. come out 出版，发行，发现； come across偶然遇到，碰到；come about 发生，产生；come up 想出，提出。故答案应为C。