What are you basing this theory on?
你這種理論的根據是什么？
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?
你到底想對我說什么？
What are you doing with those matches? Give them to me.
你拿那些火柴做什么？把它們交給我。
Dear oh dear! What are you going to do now?
哎呀呀，你現在怎么辦呢？