单项选择题
A.protect the pump from fine soluble contaminants
B.prevent solid particles from entering the pump
C.prevent solid particles from entering the filter
D.protect the directional control valves
单项选择题 On which of the following heated surfaces of a flash type evaporator would you be more likely to find soft scale formation?（）
单项选择题 Machinery operating features are designed to help conserve energy.Which of the following results will not contribute to energy conservation?（）
单项选择题 A refrigerant with oil in solution has a （）.