Initially all these filter properties were optional.

开始时所有这些过滤器属性都是可选的。

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This paper also discussed the effect of electret on filter properties.

文章还讨论了驻极电介质对空气过滤性能的影响。

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Explains how to add and filter properties on objects by using Automation Extenders.

解释如何使用自动化扩展程序添加和筛选对象上的属性。

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