单项选择题
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
单项选择题 Which of the listed sections of an emergency switchboard is used to supply power for alarm signals under emergency conditions?（）
单项选择题 When the current in a power transmission line is increased, the power loss （）
单项选择题 An operational amplifier, as used in todays consoles, may have a calculated gain of 5√This means that as the input changes by （）