单项选择题
A.draw the liquid in；force the liquid out
B.force the liquid out；draw the liquid in
C.suction；draw
D.deliver；outlet
单项选择题 The amount of fluid delivered by a helical pump can be regulated by （）.
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 （）.