A:that ; where
B:why; because
C:which; that
D:why; that
-7℃比-3℃还要____
____ ____ both cooks. They like cooking very much.
一根长为L,横截面积为S的金属棒,其材料的电阻率为ρ。棒内单位体积自由电子数为n,电子的质量为m,电荷量为e。在棒两端加上恒定的电压时,棒内产生电流、自由电子定向运动的平均速率为v。则金属棒内的电场强度大小为( )