单项选择题
Usually the panels are interlocked with （） so that the devices can be made dead before the doors are opened.
A.protective earth
B.isolators
C.ground switch
D.circuit-breakers
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In （） the control action is independent on(of) the output.
A.a closed loop control system
B.an open loop control system
C.a boiler control system
D.a steering gear control system -
单项选择题
This arrangement is （） if the elements are directly connected to one another and the control action takes place without human involvement.
A.a manual closed loop
B.a manual opened loop
C.an automatic closed loop
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单项选择题
Bourdon Tube is probably the most commonly used （） measuring instrument.
A.the absolute pressure
B.the gauge pressure
C.the vacuum pressure
D.the differential pressure
