单项选择题
An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.
A.oil foaming in the compressor B.higher than normal suction and discharge pressures with a higher box temperature C.higher than normal discharge pressure with a normal box temperature D.the compressor to run continuously
单项选择题 When the steering gear is in operation, you should （）.
单项选择题 The oil in a cargo winch gear box should be sampled periodically to （）.
单项选择题 A spur gear pump should be operated with the discharge valves （）.
