单项选择题
Moisture in a refrigeration system can cause （）.
A.freezing the expansion valve closed B.corrosion of system piping C.improper temperature regulation D.all of the above
单项选择题 When the propeller blades are integral with the hub, the propeller is called a （）.
单项选择题 The tendency of a flammable liquid to vaporize is indicated by its （）.
单项选择题 Moisture in the refrigerant may （）.
