Fathers are not optional, though.

然而父亲可不是可有可无的。

youdao

If V6.0 and earlier, this is not optional.

如果是V6.0和更高版本，则不是可选的。

youdao

The integrity function is not optional.

完整性功能不是可选功能。

youdao

I want to just go over the requirements of the course that really are required, not the optional piece, just so that you understand what my purpose is pedagogically.

我只想跟大家回顾一下,这门课程的必须要求，并非可以自由选择的,这样你们会理解我的目的何在。

耶鲁公开课 - 1945年后的美国小说课程节选

So I'm not suggesting that it's an optional problem set that you shouldn't do.

一个可做可不做的问题集,因为不做它你会后悔的。

麻省理工公开课 - 计算机科学及编程导论课程节选

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

Some thought the products were not optional, the bureau said, or that the products were free.

FORBES: What's In Your Wallet? If It's a Capital One Card, You May Be Due a Refund

It is strategic and necessary that the U.S. makes this investment and recognizes a strong industrial sector is not optional.

FORBES: High Tech Manufacturing Knowledge Should be Protected Like Fort Knox

Let me amend that: Innovation is not optional in today's economy.

FORBES: Commentary