单项选择题
采煤工作面进风流中,CO2浓度不得超过()
A.0.5% B.0.65% C.0.75% D.1%
A.0.25 B.2 C.4 D.6
A.1/3 B.2/3 C.1/2 D.4/5
A.95%~105% B.105%~2110% C.110%~115 D.115%~120%
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