“我不知道他们为什么离开，”他悲伤地说。

"I don't know why they left," he said dolefully.

《柯林斯英汉双解大词典》

你难道不想知道他们为什么这么成功吗？

Don't you want to know why they are so successful?

youdao

他们为什么要看自己知道的品牌，然后把一个新品牌带回家呢？

Why would they look at brands they knew and take home a new brand instead?

youdao

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

And they attribute it to the fact that, for all sorts of reasons, the ugly kid just matters less to the parent.

他们把这个现象归因为，不知道为什么，父母就是没那么喜欢丑小孩。

耶鲁公开课 - 心理学导论课程节选

The theory doesn't try to explain why they separated. We don't know Perhaps it was disaffection.

这一理论并着力解释他们为什么分离，我们不知道,也许是因为逆反之意。

耶鲁公开课 - 旧约导论课程节选