I.用适当语法形式或词汇填空。从A、B、C、D四个选项中选出一个最佳答案，并将所选答案的字母写在答题纸相应的位置上。(本大题共20小题，每小题1分，共20分)

1.I didn’t see Jack at the meeting yesterday afternoon.He ______ it.

A.mustn’t attend

B.can’t attend

C.mustn’t have attended

D.can’t have attended

2.It is essential that this application form ______ as soon as possible.

A.being returned

B.be returned

C.to be returned

D.will be returned

3.You ______ quit your job until you find another one.

A.had better not

B.had better not to

C.had not better

D.had not better to

4.There are more than sixty proposals ______ at the conference.

A.discussing

B.been discussed

C.to discuss

D.to be discussed

5.______ for their help,we couldn’t have finished the task ahead of time.

A.If it were not

B.Hadn’t it been

C.Had it not been

D.If it was not