Question

He must have finished the work by himself by the end of last month,____he?

He must have finished the work by himself by the end of last month,____he?
为什么填hadn't啊？为什么不填hasn't?为什么不填didn't?谢谢！
原句是must have ……，也就是说是现在完成时，那应该填hasn't啊，但为什么不填这个？
什么时候又可以用didn't?

Answer 1

by the end of last month,这是这个句子中的时间状语，意思是在上个月底之前。整句意思是他一定在上个月底前就自行完成了工作。根据意思也能知道这个句子的时态是过去完成时，但为什么原句中用的是have finished 而没有用had finished?很简单，因为前面有个must！跟在must后的动词或助动词必须是原形，所以原句中的have finished是从had finished变化过去的，这下明白了吧。

Answer 2

要根据整个句子的时间状语来选择这类反意疑问句的助动词.
1. 如果没有任何时间状,可以用have或has.
eg. He must have gone to the library, hasn't he?
2.如果有表示过去的时间状语则用did.
eg. He must have read this book last term, didn't he?
3. 如果时间状是by the end of 加过去的时间，则用had.
eg. He must have finished the task by the end of last month, hadn't he ?

Answer 3

应该是by the end of last month的关系吧，它是过去完成的一个标志，所以这里用hadn't he.如果说是last month，那么用didn't.

Answer 4

上个星期的事情，应该用过去式have的过去是是had

Answer 5

Haven't he?