For what purpose,reason,or cause; with what intention,justification,or motive:为什么
a) Why are you late?你为什么迟到?
b) Why hasn't he come?他为什么还没来?
conj.
1.The reason,cause,or purpose for which:为了哪个原因/原因
c) I know why you left.我知道他为什么走.
d) Nobody understands why she left him.没有人知道她离开他的原因.
2."why are you here?" 你为什么会在这里?