单项选择题
A.has continuously for a long period
B.suction pressure is below normal
C.oil level is below normal
D.starts after a long idle period
单项选择题 Strainers are commonly used in hydraulic systems to （）.
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?（）