为什么用what happened 而不是 what happen

I asked him what had happened 为什么要用had happened 而不直接用happened 为什么用what happened 而不是 what happen What happened to the priceless works of art?为什么不能用“They were destroyed in the earthquakeWhat happened to the priceless works of art?为什么不能用“They were destroyed in the earthquake.”回答.而要用The earthquake destroyed what happened 为什么不可以用 what did happen请一定要懂的来啊 what was happened 为什么不能用what was happen What happened to the priceless works of art?为什么不能用“They were destroyed in the earthquake.”回答.而要用The earthquake destroyed them.”求详解 what has happened 中为什么要用has 而不用have what has happened?为什么用HAS 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. You look a bit worried.What has happened?---So I do.You see,the computer I got___yesterday doesn't wore again.为什么用repaired,而不能用it repaired What happened next?这句话对吗?为什么要用happened如果是what happens next?或者what will happen next? what happened to him yesterday.为什么要用happened?happen可以吗 I don’t know what ___ last night.用he happened 还是happened to him 为什么 I still remember what happened to me.为什么what不能用that what happened about the cinema为什么用about不用 to what happened to the house?为什么用to She might have been exactly like that whether nothing had happened中为什么不能用whether而要用if? 为什么有what happened却没有what happening,而只能是what is happening,两个动词能叠加一起?最近钻牛角尖了,中学时代能理解的句子现在都掌控不了了.