Using antibiotics to kill Toxoplasma, a parasite that attacks animals

Which of the following most logically completes the argument below?

Using antibiotics to kill Toxoplasma, a parasite that attacks animals with a weak immune system, presents a difficulty: how to keep the immune system from being damaged along with the parasite. For at least some species of animals, a special medicine that prevents antibiotic-based damage of the immune system, is being developed. This protection wears off as the animal matures. Therefore, the special medicine will be especially useful for Toxoplasma-vulnerable animals that _____________ .


(A) carry their newborn babies inside of them over an extended period of time, as elephants do

(B) produce chemicals simulating the effect of the special medicine after several treatments

(C) produce, as they develop beyond puberty, immune cells strong enough to keep Toxoplasma from surviving

(D) are raised in large-scale indoor confinement operations, as chickens are

(E) are kept outdoors inhabiting free-ranging environments