[quote="yavasani"]In the major cities of industrialized countries at the end of the nineteenth century, important public places such as theaters, restaurants, shops, and banks had installed electric lighting, but
electricity was in less than one percent of homes, where lighting was still provided mainly by candles or gas.
(A) electricity was in less than one percent of homes, where lighting was still
(B) electricity was in less than one percent of homes and lighting still
(C) there had been less than 1 percent of homes with electricity, where lighting was still being
(D) there was less than 1 percent of homes that had electricity, having lighting that was still
(E) less than one percent of homes had electricity, where lighting had still been
"at+time indicator" can go with past perfect. this is shown in choice A. normally, we see "by+time indicator" goes with past perfect.
"there had been" in choice C is incorrect because "at the end of the nineteen century" , the fact that less than 1 percent of the homes had electricity still existed. that fact can not be finished at this point of time.
while at the end of the nineteen century, the installing had finished.so, "had installed " is correct.
to justify the use of past perfect, ask ourself " at this point of time, the action finished or not'
if two event happen in order , one after another, we still use two simple past tenses because we do not know whether the first event finished when the second event happen.
I learned English and I learned French
it is unclear when I learned french, I finished learning english
I had learned english and I learned French
it is clear that when I learned frenche, I finished learning english.
it find past perfect hard.