Laboratory rats and mice live up to 40% longer than usual when fed a diet
of at least 30% fewer calories than that which they would normally eat, but that otherwise contains all necessary vitamins and nutrients.
(A) of at least 30% fewer calories than that which they would normally eat, but that otherwise - than THAT which they would normally eat
a diet...THAT otherwise contains all necessary nutrients
The first that refers to the DIET NORMALLY EATEN BY RATS.
The second that refers to the DIET THAT HAS FEWER CALORIES but otherwise contains all necessary nutrients.
Within the context of a single modifier, the same pronoun -- THAT -- cannot serve to replace two different referents (the two different diets).
(B) with at least 30% fewer calories than what they would normally eat though otherwise it - "Diet with" is unidiomatic ; the usage of what conveys that rats normally would eat something OTHER THAN CALORIES.
As a result, B illogically compares CALORIES to something OTHER THAN CALORIES
(C) that has at least 30% fewer of the calories than they would normally eat, but otherwise it - Option B and C seem to imply the following contrast:
Laboratory rats live longer, EVEN THOUGH their diet contains all necessary nutrients.
Not the intention.
The intended meaning is as follows:
Laboratory rats live longer when fed a diet THAT contains all necessary nutrients.
(D) that has at least 30% fewer calories than they would normally eat but that otherwise - Correct
(E) that has at least 30% fewer calories than that which they normally eat, though that otherwise - same as A
Answer D
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