单项选择题 If a refrigeration compressor is running continuously without lowering temperature as normal in the refrigerator, the trouble may be （）.

单项选择题 Thermostatic expansion valve are （）.

单项选择题 When a hydraulic vane pump is working, which of the following is in contact with the vanes?（） (1) the rotor (2) the internal surface of the housing (3) the external surface of the housing