Which of the conditions listed represents the greatest effect of excess frost accumulation on the evaporator coils?（）

单项选择题When the vessels steering wheel on the navigation bridge is turned, the difference existing between the position of the wheel and that of the rudder is known as （）.

A.proportional band
B.the error signal
C.the reset signal
D.feedback

单项选择题Which of the listed statements is correct concerning refrigeration systems?（）

A.Dehydrators must be used continuously in a refrigeration system
B.A 25 ton refrigeration system has the same cooling effect as melting 25 tons of ice in 24 hours
C.A thermostatic expansion valve is used to control refrigerated space temperature
D.The liquid receiver functions to collect and remove non- condensable gases

单项选择题By which of the following means is force efficiently provided to vary the pitch of the blades on a modem controllable pitch propeller?（）

A.Hydraulic
B.Mechanical
C.Pneumatic
D.Electrical

单项选择题Which of the following statements concerning energy is correct?（）

A.Energy can be created or destroyed
B.Energy may not be transformed
C.The total quantity of energy in the universe is always the same
D.None of the above

单项选择题In a compression refrigeration cycle, the temperature of the liquid refrigerant experiences its greatest decrease in the（）.

A.evaporator
B.compressor
C.expansion valve
D.condenser