单项选择题
In an operating refrigeration system low on refrigerant, a liquid line sight glass will（）
A.be clear B.be blue C.be light green D.show bubbles
单项选择题 The thermal expansion valve reacts directly to the （）
单项选择题 One function of the thermal expansion valve is to（）
单项选择题 Constant superheat is maintained at the evaporator outlet of a refrigeration coil by a（）
