51. He must have had an accident, or he _A_ then.
A would have been here B had to be here C should be here D would be here
must have + 过去分词 表示对过去行为的肯定推测；
与过去事态相反用：情态动词 + have + 过去分词 来体现虚拟语气；
must 一定，必须； needn't, don't have to 不必；
53. You _A_ all those calculations! We have a computer to do that sort of thing.
A needn’t have done B must not have done
C shouldn’t have done D can not have done
should have + 过去分词 本应该，本应当； shouldn't have done本不应该，本不应当；
44. It was very kind of you to do the washing-up, but you _D_ it.
A mustn’t have done B wouldn’t have done
C mightn’t have done D didn’t have to do
52. It was essential that the applications forms _C_ back before the deadline.
A must be sent B would be sent C be sent D were sent
It be essential that 后面一定用虚拟语气，且句子谓语动词固定为(should) + 动词原型；
It was essential that the applications forms send back before the deadline.
53. We _D_ our breakfast when an old man came to the door.
A just have had B have just had C just had D had just had
when 还可以表示①刚..就… （有动作先后关系）、②恰在此时；
44. I had just started back for the house to change my clothes _D_ I heard voices.
A as B while C after D when
45. I felt somewhat disappointed and was about to leave, _C_ something occurred which attracted my attention.
A unless B until C when D while
64. It was essential that these application forms _D_ back as early as possible.
A must be sent B will be sent C are sent D be sent
- 考试辅导
