军队还没有提供对该事故如何发生以及为什么发生的解释。

The army has not yet proffered an explanation of how and why the accident happened.

《柯林斯英汉双解大词典》

那这些都是怎么发生，为什么发生的呢？

So how did it happen, and why?

youdao

那件事为什么发生？

Why did that happen?

youdao

Why are they different? How did they come that to be different? What might have happened?

两句话为什么不同,怎么会不同，可能发生了什么？

麻省理工公开课 - 媒体、教育、市场课程节选

Why did God place the stupid fruit in the garden in the first place if he knew in advance that Adam and Eve were going to eat the thing?

如果他事先就知道偷食禁果的事情会发生,为什么还要把这个不祥的果实就那么放在园子里？

耶鲁公开课 - 弥尔顿课程节选

When and why, you may ask, did this differentiation occur?

你也许会问，什么时候，为什么有这种区分的发生？

耶鲁公开课 - 旧约导论课程节选