The brass surface must be free of contamination.

黄铜表面必须未经沾污.

辞典例句

Also, be sure all insulators are kept clean and free of contamination.

而且, 还要确保所有的绝缘体清洁、不受污染.

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Be sure all components and connectors in the test system are clean and free of contamination.

确保测试系统中的所有元件和连接器清洁、无污染.

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