单项选择题
A、0.4MPa<P≤0.8MPa B、0.2MPa<P≤0.4MPa C、0.01MPa≤P≤0.2MPa D、P<0.01MPa
A.0.5 B.0.3 C.1.0 D.0.7
A.30 B.40 C.50 D.60