单项选择题
A.change in the impeller diameter
B.square of the impeller radius
C.cube of the impeller diameter
D.impeller efficiency for large changes in its size
单项选择题 Which of the following best describes the thermodynamic effect on the pressure and volume relationship with regards to saturated gases?（）
单项选择题 To operate a centrifugal fire pump at reduced capacity, you should （）.
单项选择题 An AC synchronous transmission type remote steering control system consists of a （）.