求教这道gwd语法试题

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

这个道试题答案是c, 请问D是否因为their多余而错了? more fuel-efficient small cars 和C 里的small cars that are more fuel-efficient than 这里是否都正确???

请不吝赐教,谢谢~

who can explain it ,thanks

more efficient

not more cars