单项选择题
A.55% B.50% C.84% D.90%
A.一户 B.二户 C.三户 D.四户
A.与胶管项部平齐 B.离开胶管项部2-3mm C.离开胶管项部4-5mm D.覆盖胶管项部
A.清管阀 B.分流阀 C.放空阀 D.排污阀
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