单项选择题
The pressure head of a pump is given in the unit of （）.
A.kg B.MPa C.meter fluid column D.None of the above is true
单项选择题 A gear pump belongs to （） according to its working principle.
单项选择题 Gear pumps are of positive displacement type pumps because they discharge a near constant amount of liquid （） pressure.
单项选择题 The gear and screw pumps are classified as （）.
