If they are not chosen for a trial after a day, they are not required to return.

VOA: special.2009.08.31

I have it on reserve, but that's not required for the mid-term; it's just if you're interested in seeing it.

我将其列为推荐书目,但不作为期中考试要求,如果你们感兴趣的话可以去读一下

耶鲁公开课 - 金融市场课程节选

These are completely optional, not required for the course, so there's no obligation for you guys to get involved in these things, but I'll mention these things as we go along in case anybody would like to get involved in working with professors or graduate students.

这些都是自愿选择的,而不是课程要求,所以并不强制你们都参加,但随着课程的进行,我还会不断提及,便于任何感兴趣的同学,能够与教授或研究生一同参与研究

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

Private employers are not required to pay workers for their time on a jury.

VOA: special.2009.08.31

Gray stressed that, while the justice secretary was required to consider the application for compassionate release, he was not bound to grant it.

VOA: standard.2009.08.24

Nominations for non-permanent seats are not required, countries simply announce their intention to run.

VOA: standard.2009.10.15