燃气用聚乙烯管道焊接技术安全规程。

Safety Regulation on Welding Technology for Gas …

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安全技术操作规程是安全教育的主要内容。

Safe technology operating rules is the main content of safe education.

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安全技术操作规程是安全教育的主要内容。

Safe technology operating rules is the main content of safe education.

youdao