单项选择题
A.DN25 B.DN40 C.DN50 D.DN65
A.0.3m B.0.6m C.0.8m D.0.9m
A.0.5m B.0.75m C.0.8m D.1.0m
A.2.5m B.3.0m C.3.5m D.4.0m
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