--- Please tell James that he has got the highest mark in the final examination.

--- _______. He never did so well before.

A．Congratulations

B．That’s what I expected

C．What a pleasant surprise

D．That’s right

家庭电路两端的电压是一定的，你家中同时工作的用电器越多时，相当于增大了导体的横截面积，总电阻越      ，根据欧姆定律可知，干路（进户线）电流就越        。