What are you basing this theory on?
你这种理论的根据是什么？
What are you doing up at this late hour?
深更半夜的，你在做什么？
Exactly what are you trying to tell me?
你到底想对我说什么？
What are you doing with those matches? Give them to me.
你拿那些火柴做什么？把它们交给我。
Dear oh dear! What are you going to do now?
哎呀呀，你现在怎么办呢？