Certain courses are compulsory, others are optional.
某些课程是必修的，其他是选修的。
You took an optional course this semester, didn't you?
你这学期选了一门选修课，是吗？
It is said that in England death is pressing, in Canada inevitable and in California optional.
据说，在英国死亡是迫在眉睫的，在加拿大死亡是不可避免的，在加州是可以选择的。
In the new curriculum, some courses are compulsory, while others are optional for middle school students.
在新课程中，一些课程是必修课，而另一些是中学生的选修课。
Schools in our city provide a variety of optional classes to cater to students of different levels.
我们市里的学校提供各式各样的选修课，以满足不同水平的学生。
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。
There is a tour guide throughout the trip who will organize optional dinners and sightseeing.
有一位全程导游，可安排非强制性的进餐和观光。
Optional extras include cooking classes at a top restaurant.
可选的额外之物包括一家高级餐馆的烹饪课程。
Other bath accessories, such as a loofah sponge, or bath gels, or potpourri, are very optional.
洗澡需要的其他东西，比如丝瓜络、沐浴液、精油都是可选的。
Somewhere along the line, holiday tipping went from an optional thank-you for a year of services to a Mafia-style protection racket.
一路走来，节日小费从对一年的服务表示感谢的选择变成了黑社会性质的勒索保护费。
Others believe that going to classes should be optional for students.
另一些人认为学生应该可以选择去不去上课。
According to Professor Johnson, we don't have to read the book if we don't want to, as it is optional.
根据约翰逊教授的说法，我们不想读这本书，就不必读，因为它是选读的。
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。
Inwrap device was one of the optional equipments.
包装设备是可选设备之一。
This completes the optional portion of this exercise.
这个练习的可选部分也完成了。
It contains an optional description.
它含有一个可选描述。
This model should be sufficiently valid to support optional simulation.
此模型应该足够有效以支持可选的模拟。
Otherwise, this parameter is optional.
否则，这个参数是可选的。
The cycles are periodic and optional.
循环是阶段性和可选择的。
Actions and predicate are optional.
动作和断言是可选的。
Complete the optional fields as needed.
根据需要填写可选字段。
It is optional but useful to model partitions.
建模划分是可选的但是有用的。
These attributes are optional.
这些属性是可选的。
You can even make fields optional or required.
甚至还能将字段设置为可选或必需的。
This rule states that comments are optional.
此规则声明，注释是可选的。
The square brackets ([ and ]) enclose optional parameters.
方括号（[和 ]）中的是可选参数。
新可选字段？
Hides channels with no new content (optional).
隐藏没有新内容的频道(可选)。
An optional redundant HMC configuration is supported.
支持一个可选的冗余hmc配置。
其他模板是可选的。
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