学生不必担心什么时候使用某些特定的表达。

Students should not worry about when exactly to use certain expressions.

youdao

尽管“干杯”很受欢迎，但它被认为是一种非正式的表达感谢的方式——这也就明确说明了什么时候使用它是最合适的。

"Cheers", despite its popularity, is considered an informal way to say thank you—and this is a definite clue as to when you can best use it.

youdao

为何有六层标题，什么时候使用合适？

Why were there six levels of heading, and when was it appropriate to use each of them?

youdao

So, I'll just fast forward through that, but look the point really I was trying to make, is there anything else inappropriate here?

所以，我就很快地使用了那个软件，我正要使用的时候，这里有什么不恰当的地方不？

哈佛公开课 - 计算机科学课程节选

What we do is speak, and when we speak, of course, we say correctly that we "use" language, but we still need to know what language is and we need to understand the relationship between language and speech.

我们所说的，我们什么时候说，当然，说我们这是在使用语言，但是我们仍然要理解语言到底是什么,我们要理解语言和话语的关系。

耶鲁公开课 - 文学理论导论课程节选