zěn me
这是怎么回事？
Zhè shì zěnme huí shì?
What's going on? / What's this all about?
这个问题该怎么解决？
Zhège wèntí gāi zěnme jiějué?
How should this problem be solved?
他怎么还不回来？
Tā zěnme hái bù huílái?
Why hasn't he come back yet?