单项选择题
The amount of fluid friction or internal friction inherent in a mineral lubricating oil is reflected as a measure of its （）.
A.specific gravity B.viscosity C.S E number D.hydrolytic stability
单项选择题 The major source of chemical contaminants in hydraulic fluid is （）.
单项选择题 If the thermal bulb of an expansion valve is incorrectly placed at the center of the coil instead of the end, it will （）.
单项选择题 Which of the listed pumps is NOT a positive displacement pump?（）
