Today’s technology allows manufacturers to make small cars more fuel-efficient now than at any time in their production history.
A. small cars more fuel-efficient now than at any time in their
B. small cars that are more fuel-efficient than they were at any time in their
C. small cars that are more fuel-efficient than those at any other time in D. more fuel-efficient small cars than those at any other time in their
E. more fuel-efficient small cars now than at any time in

ans is C
what's wrong with D?