If you are not yet , you are forbidden to visit this site . A.eighteen years B.at age of eighteen C.eighteen – year-old D.eighteen years of age 答案:D如图所示的电路中,电源电压不变,开关S闭合,灯L1和L2都正常发光.一段时间后,突然其中一灯熄灭,而电压表和电流表的示数都不变,出现这一现象的原因可能是( )A.灯L1短路 B.灯L2短路 C.灯L1断路 D.灯L2断路