So they're optional, but they're very, very, very highly encouraged that you do these, because this is going to give you practice for the types of problems that are going to be on the exam.

虽然它们是选做的，但是它们非常非常，非常值得你们去做，因为这对你们来说是一次训练,是用来熟悉考试题型的。

麻省理工公开课 - 化学原理课程节选

Nobody else has to read this, this is just for your own personal practice.

别人不用读你的日记，这只是你自己的练习。

英语写作：技巧 - SpeakingMax英语口语达人

I'm gonna run a.out and your teaser for the kinds of programs you can write after years and years and years of practice will give you output like this.

运行a，out，这类麻烦的程序,你多年多年之后也能写,因为最后的结果是这样的。

哈佛公开课 - 计算机科学课程节选