单项选择题
A.O2≤0.5% B.O2≤5% C.O2≤0.2%
A.0.75~0.8Mpa,0.8~0.9Mpa B.0.6~0.85Mpa,0.7~0.75Mpa C.0.4~0.6Mpa,0.6~0.7Mpa
A.70% B.20% C.50% D.30%