And what we saw last time is that this was necessary to make things work, this part of it in particular.

上节课我们讲,这是对外做功的必要条件，特别是这个部分。

麻省理工公开课 - 热力学与动力学课程节选

The fact that I have this star here, this star here, this star here, is really just 'cause I'm a little anal and it looks pretty to make a little box out of everything but it's not strictly necessary.

事实上大家可以看到，这有颗星，这有颗星，这有颗星，其实是我手痒,这看起来像是用*围成个框，把它们包围起来,其实这是完全没有必要的。

哈佛公开课 - 计算机科学课程节选

Why is it necessary to rend something, to make it soul or whole? Is it necessary?

为什么要撕破某样东西，它才能完美呢，这有必要吗？

耶鲁公开课 - 现代诗歌课程节选