单项选择题
A.throttling the pressure line
B.changing the speed of the rotor
C.either A or B
D.None of the above is tree
单项选择题 Which of the following pumps are self-priming, and can deal with liquid from a level below the pump? （） (1) reciprocating (2) rotary (3) centrifugal
单项选择题 The amount of fluid delivered by a positive displacement pump can be regulated by （）.
单项选择题 The amount of fluid delivered by a reciprocating pump can be regulated by （）.