In a data communication system, the transport media with the widest frequency band and best reliability is the( ).

A:radio channel B:coaxial cable C:twisted--pair cable D:fiber optic cable

In the closed cooling system, the water _____.

A:is made to circulate out of the system B:is made to circulate within the system C:is made circulate within the system D:is made circulate out of the system

In an auxiliary boiler steam and water system, the highest pressure will be in the _____.

A:steam stop valve B:dry pipe C:feedwater system D:generating tubes

The refrigeration system low pressure cutout switch is actuated by _____.

A:an electric system manager B:a sensing bulb at the tail coil of the evaporator C:pressure changes in the suction line D:failure of the king solenoid valve

After installing a new hydraulic pump in a system, what special attention should be given to the hydraulic system?

A:The relief valves in the system should be readjusted B:The filters and strainers should be checked frequently C:All system pressure should be readjusted D:The system should be drained and renewed with a fluid of different operatingcharacteristics

Moisture in a refrigeration system can cause _____.

A:freezing the expansion valve closed B:corrosion of system piping C:improper temperature regulation D:all of the above

Pressure in an operating hydraulic system is developed _____.

A:only by the pump as its primary function B:by resistance to the fluid flow through the system C:by the thermal input to the systems fluid D:solely by the charge applied by the accumulators

Purging air from a hydraulic system is necessary when .

A:adding small amounts of oil to the system B:the system has been overheated C:the system has been drained and then filled with new oil D:the system has been idle for a long period of time

Which system(s) in the hydraulic systems of crane always hold(s) single side of load?

A:hoisting system only B:hoisting system and luffing system C:hoisting system and slew and slewing system D:slewing system only

The IALA buoyage system is divided into two categories______．

A:The buoy system and the lighthouse system B:The central buoy system and the side buoy system C:The lateral system and the cardinal system D:The stripe system and the band system"