15. By installing special electric pumps, farmers’ houses could be heated by the warmth from cows’ milk, according to one agricultural engineer.(A) farmers’ houses could be heated by the warmth from cows’ milk, according to one agricultural engineer (B) the warmth from cows’ milk could be used by farmers to heat their houses, according to one agricultural engineer (C) one agricultural engineer reports that farmers could use the warmth from cows’ milk to heat their houses (D) farmers, according to one agricultural engineer, could use the warmth from cows’ milk to heat their houses (E) one agricultural engineer reports that farmers’ houses could be heated by the warmth from cows’ milk
Personally, I think the logic meaning is the key in this case.
1. special electric pumps ---- one engineer, not as good as farmers 2. by installing ------- one engineer reports, it's illogic. probably, one engineer finds or suggests that... is better.