单项选择题
A liquid indicator sight glass is useful in determining whether or not a refrigeration system is sufficiently chargedIt is generally located in the（）.
A.high pressure liquid line B.low pressure liquid line C.high pressure vapor line D.low pressure vapor line
单项选择题 Compared to a constant pitch propeller, a controllable pitch propeller（）.
单项选择题 Which of the following statements describes the functions of a reservoir used in a hydraulic system?（）
