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
单项选择题 In （） the control action is independent on(of) the output.
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.
单项选择题 Bourdon Tube is probably the most commonly used （） measuring instrument.
