二极管D和灯泡HL相串联,电路如图5.5所示。设电源电压 ,且二极管的正向压降及反向漏电流可忽略,则灯泡两端的电压平均值U AB为( )。
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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