Sentence Correction

Poor people, who already purchase the cheapest food items - starches, frankfurters, beans and the like - have no items that they can economize when there is a rise in overall price of food.

A) that they can economize when there is a rise in overall price of food
B) on which there can be economizing when there is a rise in overall price of food
C) for economizing if there will be an overall rise in the price of food
D) on which to economize when overall prices of food rise
E) that can be economical when overall prices of food rise

I chose E, but OA is D..

My two cents:

First thing to notice: Economize on is an idiom.so out of A,Band C are out..B because it is wordy.
Now things do not BECOME economical, they become affordable. If it were "affordable" I would have gone for it..

Hope it helps..