单项选择题
A.5 B.7 C.10 D.20
A.1~2s B.5~10Min C.15~20s D.20~30s
A.0.1MPa B.0.5MPa C.1.0MPa D.1.5MPa
A.100m3 B.400m3 C.1000m3 D.2000m3
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