--What on earth are the police busy with?-They have been looking into how the plane cra

问题补充：

--What on earth are the police busy with?

---They have been looking into how the plane crash .

A. came out

B. came up

C. came down

D. came about

答案：

A. came out

B. came up

C. came down

(答案→)D. came about

解析：考查短语辨析。come out 开花，出版，come up 走近，上来，被提出，come down 降低，下来，come about 产生，发生.答语的意思为：他们在一直调查飞机坠毁是怎么发生的。所以答案选D 。