you和they用are she,he,it用is where are you going?为甚么不能是 where is you going?

you和they用are she,he,it用is where are you going?为甚么不能是 where is you going?
you和they用are she,he,it用is where are you going?为甚么不能是 where is you going?

you和they用are she,he,it用is where are you going?为甚么不能是 where is you going?
be动词的固定搭配,没有为什么