题目: 有一横截面积为S的铝导线,当有电压加在该导线上时,导线中的电流强度为I。设每单位体积的导线中有n个自由电子,电子电量为e,此时电子定向移动的速度为v,则在△t时间内,通过导体横截面的自由电子数目可表示为[ ]A.nvS△t B.nv△t C. D. 答案: AC
题型:选择题 My son has changed so much that I could hardly __________ his voice on the phone.A.recognizeB.realizeC.hearD.find 查看答案