单选题While paralleling two AC generators using synchronizing lamps only, both lamps will go dark when the generators are （）.Arunning at the same speedBgroundedCof the same polarityDin phase
单选题
While paralleling two AC generators using synchronizing lamps only, both lamps will go dark when the generators are （）.
A
running at the same speed
B
grounded
C
of the same polarity
D
in phase
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