A:must happe
B:should have happened
C:could have happened
D:must have happened
区别O2与CO2的方法很多,下列方法不能用来区别O2与CO2的是
一台水泵每秒钟内可把76.5kg水扬高10m,带动水泵的电动机的输入功率为12kW,电动机的效率是85%,g=10N/kg,则水泵的效率是____。