单项选择题 The advantage of a centrifugal pump as compared with a reciprocating pump is that （）.

单项选择题 A pump is said to have "negative suction head" when the pump is located （）.

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) vane (3) gear