I also have a question about D)
Conclusion says "that
less gasoline is being used as a result of the operations of these households
than they would have used if they had maintained their original cars"
It says "Electric companies use gasoline powered generators to produce
at least some of the electricity they provide to their customers"
So even with D saying that "at least some electricity is produced with gasoline", when comparing the scenario of 1) Use electric car and 2) Still use gasoline car -> scenario 1) will result in less if not the same gasoline consumption comparing to scenario 2)
Choice D sounds like inference answer to me than a weakener.
Please point where did I get it wrong. Thanks!