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

你这学期选了一门选修课，是吗？

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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。

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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。

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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).

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