As in D and E, more fuel efficient small cars means tht...increasing the quantity of the cars rather than...increasing the fuel efficiency...
thts y eliminating D and E
In A and B, "their" pronoun ambiguous..dunno, if it;s the history of the manufactuers or the history of the small cars.
C avoids these 2 mistakes...
Going for C
ARISE AWAKE AND REST NOT UNTIL THE GOAL IS ACHIEVED