Some properties are required, some are optional. Some have simple string values, some are complex resources.

一些属性是必要的，一些则是可选的。一些只是简单的字符串值，一些则是复杂的资源。

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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。

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In this process, some of the variables are primary elements that are necessary for input, while others are optional.

在这一过程中，一些变量是基本的元素，是必须输入的，而其它一些却是可选的。

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All the platforms are clearly designated, and while you may be able to explore the broader world, and while some portions of most dungeons are optional (such as loot-filled treasure-chests) for the most part you have to stick to a path clearly set out for you.

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