One major difference between electron affinity and ionization energy is that when we talked about ionization energy, remember ionization energy always has to be positive.

电子亲和能,与电离能之间最大的不同就在于,当我们提到电离能的时候，记得电离能总是正的。

麻省理工公开课 - 化学原理课程节选

Remember, "is it okay" must always be followed with either "if" or "to".

记住，使用“is it okay”时后面一定要跟上 "if" 或者"to"。

Is it okay 课堂 - SpeakingMax英语口语达人

If you have a real gas and you write du is Cv dT and your path is not a constant volume path, then you are making a mistake. But for an ideal gas, you can always write this. And this turns out to be very useful to remember.

对于真实气体，如果其变化过程,不是恒容的，du=Cv*dT就不成立，但对于理想气体,这条规则永远成立,这一点非常有用，请记住。

麻省理工公开课 - 热力学与动力学课程节选