prep的一题

In the major cities of industrialized counties at the end of the 19 century, important public places such as theaters, restaurants, shops and banks had installed electric lighting, but_________provided maily by candies or gas.

A. electricity was in less than one percent of homes, where lighting was still

B. less than one percent of homes had electricity, where lighting had still been

正确答案是A, 请问B为什么不对

where 引导的从句的时态和homes had(这里是过去式，而非完成时）不一致。

因为没有明显的暗示这两句话有先后的动作关系，所以，时态要保持一致，我想。