单项选择题
The operator of electrical motors should keep a constant check on the loads they carry because （）
A.low loads necessitate frequent insulation cleaning
B.exceeding nameplate values shortens useful life
C.energy is wasted if full loading is not utilized
D.power factor correction methods are load dependent
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Which of the listed sections of an emergency switchboard is used to supply power for alarm signals under emergency conditions?（）
A.The generator and bus transfer section
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A.1 volt, the output changes 5 volts
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D.10 volts, the output changes 5 volts
