The three backpackers finally reached the top of Mount Huangshan, ________ they could enjoy the breathtaking sights to their heart's content.

A．when

B．where

C．why

D．how

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        。