I know it's possible to induce chemical reactions, but these are exceptions. This is not the norm.

我知道催化化学反应是可能的，但是那些是特例，不是常规情况。

麻省理工公开课 - 固态化学导论课程节选

Now we can think about the fourth period, and the fourth period is where we start to run into some exceptions, so this is where things get a teeny bit more complicated, but you just need to remember the exceptions and then you should be OK, no matter what you're asked to write.

现在我们可以考虑第四周期，而且在第四周期,我们会遇上一些特例，所以事情有,一点复杂，但是你只需要记住,这些特例然后就没有问题了，无论你被要求写什么。

麻省理工公开课 - 化学原理课程节选

So the exceptions are useful when you want to have the ability to say, I expect in general this kind of behavior, but I do know there are some other things that might happen and here's what I'd like to do in each one of those cases. But I do want to make sure that I don't let a value that I'm not expecting pass through.

所以当你希望有能力说,我希望一般是这样的行为,异常是很有用的,但是我明白还有一些其它的情况可能发生,我希望对每一种情况都这么做,但是我跟希望能保证,没有让一个预期之外的情况漏过去。

麻省理工公开课 - 计算机科学及编程导论课程节选