任何非必需的变量都可以为空。

Any variables that are not mandatory can be null.

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可以通过增加一个非必需的参数，轻松地改变这个函数的用途。

You can easily repurpose this function by adding a nonrequired argument.

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基建工程，包括奥运会设施，仍按计划进行，但将削减非必需的支出。

Spending on infrastructure, including the Olympics, will continue as planned. But there will be cuts in “non-essential” spending.

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