what [ ] [happen] 用所给单词的适当形式填空

what [ ] [happen] 用所给单词的适当形式填空 为什么用what happened 而不是 what happen What happen what happen what happened?happen用过去式?详细 he walk over to see what happened...什么时候用what is happen 什么时候用what happen I don't know what ___(happen) to China in a century 用所给词的适当形式填空 No one knows what (happen) before it really happens 用所给词的适当形式填空 What happen还是What is happen? 为什么有时happen用助动词进行提问,而有时则不用?如：What will happen...What happened...What did happen...What was happening. what will happen? What happen to What's happen? What will happen? what will happen then what will happen next? What happen is incorrect? what is happen