掘进工作面的进风流中,氧气浓度应不低于20%,二氧化碳浓度不超过0.5%。
参考答案:对
— Could you help me put up the maps on the wall?
— ________
A.No problem.
B.I hope so.
C.That’s all right.
D.That’s a good idea.
蝇蛆病