Question

The teacher asked us________to do our homework．

1. A.
   didn't forget
2. B.
   not forget
3. C.
   not to forget
4. D.
   don't forget

Answer 1

C
解析：

分析：动词不定式的否定形式是not to do(如果是不带to的动词不定式，就是not do，如果要强调这种否定，也可以用never来代替not，成为never to do形式)，和动词谓语的否定结构是不同的(not总是放在谓语结构的第一个词的后面，如：am not，is not，were not，shall not，would not，have not，had not，does not，do not，did not等)。此处asked us to do结构，其否定形式应该是asked us not to do．