I Peter with his work, but I had a lot of things to do myself.
A. must have helped
B. should have helped
C. needn’t have helped
D. can’t have helped
网友回答
A. must have helped
(答案→)B. should have helped
C. needn’t have helped
D. can’t have helped
解析：本题的关键词是but后面的句中使用了一般过去时，说明本句表示的是对过去的虚拟。对过去情况的虚拟使用“情态动词+have done”的形式。Must have done一定做了某事；should have done本应该做某事，实际上却未做；needn’t have done本不需要做，实际上去做了；can’t have done不可能做某事；句义：我本应该帮助Peter做他的工作，但是我有很多自己的事情要做。AD两项并没有比赛虚拟语气，只是对过去情况的推测。C项语义不搭配。根据句义说明B正确。