单项选择题
A.容积式泵 B.离心泵 C.动力式泵 D.混流泵
A.建筑钢 B.普通钢 C.结构钢 D.特殊性能钢
A.1:4~1:5.5 B.1:5~1:6.5 C.1:6~1:7.5 D.1:7~1:8.5