C is the right answer.
This is a good question in which prephasing/anticipating what the right answer looks can help greatly. Basically, the right option should tell us one of two things:
1) Gasoline cars have increased fuel efficiency though one way or another
2) Electric cars' improved efficiency through technology has been tempered by some other factor related to electric cars.
Perform this forecasting enables us to comfortably choose C with little hesitation.
Der alte Fritz.
+1 Kudos me - I'm half Irish, half Prussian.