1. 到底何时使用did？
did和其它助动词一样，本身无意义，自己不能独立作谓语，只能和其它主要动词一起构成谓语，用于构成一般过去时的否定句和疑问句，当然也常常用于代替上文中的行为动词的过去式。如:
I didn't go to school last Sunday. 上周日我没上学。
Did you buy a new pen yesterday? 昨天你买了枝新钢笔吗？
2. did身后的动词到底用什么形式？
有的小朋友总不注意did身后的动词用什么形式，在否定句和疑问句中，
did身后的动词必须用原形。 "他昨天没有在家吃午饭。"
[误] He didn't had lunch at home yesterday.
[正] He didn't have lunch at home yesterday.
3. 我能用be动词代替吗？
不管怎么说，含有行为(实义)动词的一般过去时的肯定句变成否定句或疑问句时，不能用be动词，必须用到did！含be动词的句子构成否定句或疑问句都绝不会让
did露面！ 例句：They went to the park last week. (改为否定句)
[误] They weren't go to the park last week.
[正] They didn't go to the park last week.