But then having found one answer, you can add to it anything that gets killed by the act of taking derivatives.

一旦你算出了一个答案,你就可以往式子里加入任何,在求完导后消失的项

耶鲁公开课 - 基础物理课程节选

There's one class that... it's a club where, once you get involved, you can teach a class.

还有一种，一旦你加入了这个俱乐部，你就可以教一门课。

阿卡贝拉组合最棒 - SpeakingMax英语口语达人