在电气线路中，必须要有控制电器和保护电器，用于控制线路的通断，保护用电设备、线路、电源设备以及人身的安全。 - 查题网

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国家开放大学 / 安装工程估价

在电气线路中，必须要有控制电器和保护电器，用于控制线路的通断，保护用电设备、线路、电源设备以及人身的安全。

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人类的外周免疫器官有：医学免疫学

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