what happened 为什么不可以用 what did happen请一定要懂的来啊

what happened 为什么不可以用 what did happen请一定要懂的来啊 I asked him what had happened 为什么要用had happened 而不直接用happened what was happened 为什么不能用what was happen what happened to him yesterday.为什么要用happened?happen可以吗 recall 可以与back 连用吗I _____ back and wondered what would have happened if .答案是thought,那为什么 recall不可以?因为有back吗? I still remember what happened to me.为什么what不能用that 为什么用what happened 而不是 what happen the surprised look on her face suggested that she what had happened.为什么只能用hadn't known?should not know 不可以吗 What can have happened to her29.She's already an hour late,What _____to her A can have happened B may happen C should have happened D may have happened 为什么选A,B＼D有什么不对吗 请问what happened?这个问句成不成立?怎么可以一个助动词都没有呢? The story happened in London before the second world warhappened 那里为什么不可以用 had happened this is what happens 为什么不写成 this is what happenethis is what happens 为什么不写成 this is what happened? what has happened?为什么用HAS what happened这个句子对吗 为什么 为什么用has,括号内不填单词可以吗?no matter what (has) happened to you1.为什么用has,（我想知道的是为什么不选其他单词,只选have这个单词)2.括号内不填单词可以吗?no matter what (has) happened to you What has happened?What has happened?---I have lost my key and can't open the door.为什么不能用What happened?---I lost my key and i can't open the door.两者的区别是什么? what/that has happened.为什么是选what?happen后面不是不加宾语嘛?为什么不是that啊! Alice,would you please tell me___?A.where is mr,blackB.what is happened to uC.when did the school bus leaveD.what's your trouble为什么不可以选b 要选d?错了 是could。