He didn't answer the phone immediately as he was ( ) on a difficu_英语解答

He didn't answer the phone immediately as he was ( ) on a difficult maths problem.
A.busy to work B.busy with work C.busy working D.busying

人气：276 ℃　时间：2020-04-04 12:50:53

解答

c 必须的!为什么？谢谢！be busy doing sth 其实也可以是 be busy (in) doing sth. 意为忙于做某事。

be busy to do sth.如果是 be too busy to do sth.
那就是too...to...结构了，可以这样用，太忙了以至于不能干什么。

work on 的work做名词才是

所以c