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

你这学期选了一门选修课，是吗？

youdao

youdao

By setting Peking Opera as an optional course, students may have more freedom to decide whether to take it or not.

通过将京剧设置为选修课，学生们可以有更多的自由决定是否选修京剧。

youdao

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

"When it's an optional regulation, it's not that big of a deal, " Gradante said.

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The company just announced the Inspiron 15z, a 15-inch notebook with an optional touchscreen.

ENGADGET: Dell unveils Inspiron 15z Ultrabook with optional touchscreen, prices start at $750

This is especially useful when using the camera with an optional viewfinder (sold separately).

ENGADGET: Sony's Cyber-shot RX1 compact camera packs a full-frame sensor, 'fits in your palm' (hands-on)