原子：元素的特征性质保持不变的最小物质单元，也是在不释放带电粒子的情况下物质能够分割的最小单元。

Atom: Smallest unit into which matter can be divided and still retain the characteristic properties of an element.

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如果集合不包含使用指定名称的元素，则该集合保持不变，且不引发异常。

If the collection does not contain an element with the specified name, the collection remains unchanged and no exception is thrown.

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