单项选择题
Brushless generators are designed to operate without the use of（）.
A.brushes B.slip rings C.commutators D.all of the above
单项选择题 It （） for an emergency generator to require paralleling.
单项选择题 Usually the panels are interlocked with （） so that the devices can be made dead before the doors are opened.
单项选择题 In （） the control action is independent on(of) the output.
