I don't know how this happened.

我不知道这事怎么发生的。

《牛津词典》

Can you quote me an instance of when this happened?

你能否给我举例说明一下发生这事的情况？

《牛津词典》

This happened to my aunt when she wanted to quit her job and become a policewoman.

这件事发生在我阿姨身上，当时她想辞掉工作，去当一名女警察。

youdao

When this happened, my friend would have to go in the hole.

VOA: special.2009.10.11

Suppose the planet were hit by a comet-- this happened--something like this happened sixty-five million years ago, so it could happen again.

假设这个星球被一颗彗星击中-,这样的事，大约六千五百万年前,发生过，所以它还可能再发生。

耶鲁公开课 - 金融市场课程节选

And we'll talk about the impact of what this happened, there were obvious impacts, but what happened on civil society and on politics.

我们会谈谈这些事的影响,有一些显著影响,但是对于社会大众和政治呢

耶鲁公开课 - 1871年后的法国课程节选

The first time this happened I duly entered that permission thinking it was just something new.

FORBES: First There Was Apple's MapGate, Now Welcome ParentGate

As this happened, the US began pushing Europe off the top of the economic ladder.

BBC: Eurozone crisis: What it means for East and West

This happened now, when everybody is awake to the problems that can result from bad loans.

NPR: Woman: Countrywide Proposed Fibbing to Get Loan