adv.（用于问句）为什么；为何；（反问，表示不必）何必；（说明理由）为什么
int.呵唷，哎呀，嗨
n.理由；原因；说明；难解的问题
复数：whys
例句：
Why hasn't he brought the whisky?...
他为什么没把威士忌拿来？
Why didn't he stop me?...
为什么他没阻止我？
Why can't I remember the exact year we married?...
为什么我记不起我们结婚的准确年份了？
He still could not throw any further light on why the elevator could have become jammed...
对于电梯为什么会卡住他仍旧给不出更多的解释。
Experts wonder why the US government is not taking similarly strong actions against AIDS in this country...
专家们对为什么美国政府没在这个国家采取类似的强硬措施来对抗艾滋病而感到疑惑。
I can't understand why they don't want us.
我不明白为什么他们不要我们。
Why is also an adverb.
I don't know why...
我不知道为什么。
It's obvious why...
原因很明显。
Here's why.
这就是原因。