采煤工作面進(jìn)風(fēng)流中,CO2濃度不得超過(guò)()
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