You took an optional course this semester, didn't you?

你这学期选了一门选修课，是吗？

youdao

If you see humor as an optional form of entertainment, you're missing some of its biggest benefits: humor makes average-looking people look cute and uninteresting people seem entertaining.

如果你认为幽默只是一种可有可无的娱乐形式，那你就忽略了幽默最大的好处：幽默能让长相平平的人看起来更可爱，也能让呆板无趣的人看起来更有趣。

youdao

Finally, you can enter an optional description and category.

最后，您可以填写可选的描述和类别项。

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

They do have interviews when you apply, but they're optional.

当你申请的时候，他们确实会进行面试。不过也是选择性的。

被学问的自由所迷住 - SpeakingMax英语口语达人

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

Share capability, allowing images to be sent wirelessly to an iOS or Android device and edited with the included app -- provided you have the optional Toshiba FlashAir card.

ENGADGET

As it happens, you could configure the Revolve with Windows 7 and you could buy an optional pen to go with it, but obviously, if you'd prefer to use your fingers, you'll have a lot more luck here than you would have with earlier models.

ENGADGET: HP announces the EliteBook Revolve, a Windows 8 convertible for the business crowd (video)

Legal also has crab cakes, shrimp and lots of other optional stuff you can add.

FORBES: Mail Order Meals -- My Favorites