他总是在你最意料不到的时候出现。

He always turns up just when you least expect him.

《牛津词典》

红茶就是在这个时候出现的。

Black tea arrived at this time.

youdao

主动学习者不断地监测自己的理解，他们知道自己的理解什么时候出现了问题，在迷失方向之前就会寻求帮助。

Active learners are constantly monitoring their understanding, they know when their comprehension breaks down, and they ask for help before they become lost.

youdao

You might say, of course the question, what renders authority legitimate, is only possible, or is only raised when authority is in question.

你们可能会说，这个问题当然是，如何使权力合法化这个问题，当然是可能的，或者说当权力出现问题的时候这个问题会自然出现。

耶鲁公开课 - 政治哲学导论课程节选

and they should only make investments if there's really a--if they can see a really compelling case.

他们应在只有在,非常好的机会出现的时候,才进行投资。

耶鲁公开课 - 金融市场课程节选

It's a bad habit to get into, because when you come back to it, it may haunt you later on down the road. So really get into that notion of trying to be defensive as you program.

来运行程序的时候,错误就会出现缠住你了,因此现在我们真的要培养,在程序中有防卫性设计的概念。

麻省理工公开课 - 计算机科学及编程导论课程节选