单项选择题
A.甲烷、乙烯 B.氢气 C.一氧化碳、二氧化碳 D.乙炔
A.2mm B.2.5mm C.3mm D.5.0mm
A.350s B.200s C.400s D.150s
A.500~1000 B.250~500 C.1000~2000 D.150~250
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