Is the answer C..........

yes any rule for this...pls tell me

we are comparing cars in the sentence............than is used for comparison and "those" over here refers to the cars which used to be built earlier.............

alltimeacheiver wrote: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

The option C correctly uses "than those at any other time in production history". The other options have "in their production history" which is wrong.

C is the right answer.

The important issue with those is that when we are construing a sentence we have to make sure apples are being compared to apples and oranges are being compared to oranges.

In the original sentence the efficiency of cars is being comapred to "any time in their production history." This is WRONG. We want to compare cars built now with cars built in the PAST. By adding THOSE we know logically that the comparison is cars now and cars in the past.

Why is the comparison when THOSE is added? Simple because those in the sentence refers to the cars. With option C new efficient cars is being compared with older cars that are less efficient. So vola!