单项选择题
A.In order for a fluid to be pumped, a fluid must be made to flow
B.A substance must be cold in order for it to be pumped
C.The kinetic energy imparted by the pump can be used to force a liquid through a hydraulic system
D.A pump must receive its energy from an external source
单项选择题 Most pump manufacturers recommend that the suction piping dimension for centrifugal pumps be （）.
单项选择题 In the operation of a flash type evaporator equipped with air ejectors,the air and non- condensable gases are evacuated directly from the （）.
单项选择题 The refrigeration compressor in a water cooled refrigeration system is short cycling on the high pressure cutout switch， One reason for this could be the （）.