The reason much refrigerated food spoils is that it ends up out of sight at the back of the shelf. So why not have round shelves that rotate? Because such rotating shelves would have just the same sort of drawback, since things would fall off the shelves' edges into the rear corners. Which of the following is presupposed in the argument against introducing rotating shelves?

(A) Refrigerators would not be made so that their interior space is cylindrical.
(B) Refrigerators would not be made to have a window in front for easy viewing of their contents without opening the door.
(C) The problem of spoilage of refrigerated food is not amenable to any solution based on design changes.
(D) Refrigerators are so well designed that there are bound to be drawbacks to any design change.
(E) Rotating shelves would be designed to rotate only while the refrigerator door was open.

In this CR,the author already described the disadvantage of having circular shelf. He rejected the plan to have a circular shelf in refrigerator because the food would rot despite of having suitable shelf design. Having a circular shelf would also not help much to save the foods. Now, how come the author presupposed that the refrigerator could not be made with cylindrical inferior space.
To me, the choice C appears to be correct as it was saying that spoilage of food does not depend upon the shape of the shelf.