Today’s technology allows manufacturers to make small cars more fuel-efficient now than at any time in their production history.

1. small cars more fuel-efficient now than at any time in their
2. small cars that are more fuel-efficient than they were at any time in their
3. small cars that are more fuel-efficient than those at any other time in
4. more fuel-efficient small cars than those at any other time in their
5. more fuel-efficient small cars now than at any time in（Ｃ）

为什么Ｄ错的啊？