A.time
B.space
C.length
D.visibility
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A.the slewing motor
B.the lulling motor
C.the hoisting motor
D.none of the above
A.contraction
B.retraction
C.expansion
D.shrinkage
A.Hydraulic pumps
B.Valves
C.Hydraulic cylinders
D.Hydraulic motors
A.the slewing motor
B.the luffing motor
C.the hoisting motor
D.none of the above
A.unusual vibration
B.excessive worn parts
C.abnormal pressure
D.any of the above
最新試題
An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.
Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.
Which of the following statements is correct concerning heat transfer?（）
The temperature differential occurring between the inlet temperature of the fluid to be cooled and the outlet temperature of the cooling medium in a shell-and-tube heat exchanger is greatest in which of the flow designs listed?（）
The usual symptoms of cavitation in a centrifugal pump is （）.
The output volume of a positive fixed displacement pump can be changed only by （）.
The general purpose of a heat exchanger is to （）.
One cause of high head pressure occurring in a refrigeration system can be （）.
An increasing head pressure in a refrigeration system, without any corresponding change in the cooling water inlet temperature, would probably be caused by （）.
A pressure drop through the refrigerant liquid line may cause （）.