单项选择题
The discharge flow of a reciprocating pump is （）.
A.steady B.in pulsation C.continuous D.large
单项选择题 A centrifugal pump produces the required pressure energy by means of a rotating （） provided with vanes.
单项选择题 The pressure head of a pump is given in the unit of （）.
单项选择题 A gear pump belongs to （） according to its working principle.
