当被输送液体的密度变化时,如下特性曲线中将发生变化的有几条?()
①压头~流量曲线;
②轴功率~流量曲线;
③效率~流量曲线。
A.0
B.1
C.2
D.3
参考答案:B
The old couple have married for 40 years and never once _______ with each other.
A.they had quarreled
B.they have quarreled
C.have they quarreled
D.had they quarreled
瓦斯喷出区域、高瓦斯矿井及煤与瓦斯突出矿井中,掘进工作面的()应采用“三专供电”,即专用变压器、专用开半和专用线路。
A、掘进机
B、煤电机
C、局部通风机
D、刮板输送机