单项选择题
A.is usual B.is not usual C.is necessary D.is not impossible
Usually the panels are interlocked with （） so that the ...
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
In （） the control action is independent on(of) the outp...
单项选择题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
This arrangement is （） if the elements are directly con...
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 D.an automatic opened loop
