单项选择题
The amount of fluid delivered by a screw pump can be regulated by （）.
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 A screw pump belongs to （） according to its working principle.
单项选择题 Through a （） pump, the liquid is transferred from the suction to the discharge by the mechanical variation of the volume of a chamber or chambers.
单项选择题 In a （） the center screw is driven and the outer screws idle.
