题目

-Did you attend Mary and Tom’s wedding ceremony?   -Yes，but as you know，they________each other no more than 3 months．   A．knew    B．had known       C．have known      D．have been known   答案：B13．将小灯泡L与R=10Ω的电阻按如图所示方式连接．闭合开关S后，电压表的示数为8V，电流表的示数为1A．设小灯泡灯丝电阻不变，求：小灯泡L的电阻值．