单项选择题
A.2 B.3 C.4 D.5
A.当管径小于等于200mm,跌水水头大于0.2mm时。 B.当管径小于等于300mm,跌水水头大于0.3mm时 C.当管径小于等于400mm,跌水水头大于0.4mm时 D.当管径小于等于500mm,跌水水头大于0.5mm时
A.8 B.9 C.10 D.11