你手上怎么有绷带，发生什么事了？

Why do you have a bandage on your hand—___what happened?

你说你把手机掉进马桶了？这到底是怎么回事啊！

You dropped your phone in the toilet? ___What happened!

你看起来有点沮丧，发生什么事了？

You look upset, ___what happened?