单项选择题
A.add refrigerant to the system
B.adjust the thermal expansion valve to the proper setting
C.adjust the float valve to the proper holding pressure
D.open the hand expansion valve
单项选择题 Crankcase sweating in a refrigeration system is caused by （）.
单项选择题 In an electro-hydraulic steering system, under movement is maintained in close synchronization with the steering wheel position by means of the （）.
单项选择题 The internal force of a material, which tends to resist deformation when subjected to external forces, is known as （）.