Question

There was an accident in the factory, but no one knew who was _________ of the trouble．

1. A.
   at the end of
2. B.
   at the top of
3. C.
   in the middle of
4. D.
   at the bottom of

Answer 1

D
题意是“工厂里出现了事故，到底谁是祸首，没有人知道。”at the bottom of表示某事的根源，起因，导火索。A项，在……末端；B项，在……的顶部；C项，在……中间。