没人确切知道为什么青春期是人类独有的。

No one knows for sure why adolescence is unique to humans.

《柯林斯英汉双解大词典》

我不知道为什么。

I don't know why.

《柯林斯英汉双解大词典》

我不知道为什么所有人都为几只蚊子发这么大的牢骚。

I don't know why everybody makes such a fuss about a few mosquitoes.

《柯林斯英汉双解大词典》

So when I expand this gas adiabatically and it cools down, why do you think it might cool down?

现在我们知道了气体绝热膨胀时,温度会下载，为什么会降温？

麻省理工公开课 - 热力学与动力学课程节选

But for me, I like to look at something and just say, "I like this. I don't really know why though."

但对我来说，我喜欢看着某个东西，然后说，“我喜欢这个。但我也不知道为什么。”

关于现代美术 - SpeakingMax英语口语达人

And I don't know why, but since time immemorial that is the way computer scientists have drawn trees.

叶子是在最下面的，我不知道为什么,但从记事以来他们就是这么画树的,这也许就是为什么我们。

麻省理工公开课 - 计算机科学及编程导论课程节选