单项选择题
Gear pumps are of positive displacement type pumps because they discharge a near constant amount of liquid （） pressure.
A.depending on B.in relative to C.regardless of D.because of
单项选择题 The gear and screw pumps are classified as （）.
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 A vane pump belongs to （） according to its working principle.
