Critical Reasoning

It is probably not true that colic in infants is caused by
the inability of those infants to tolerate certain antibodies
found in cow's milk, since it is often the case that
symptoms of colic are shown by infants that are fed
breast milk exclusively.
Which one of the following, if true, most seriously
weakens the argument?
(A) A study involving 500 sets of twins has found
that if one infant has colic, its twin will probably
also have colic.
(B) Symptoms of colic generally disappear as infants
grow older, whether the infants have been fed
breast milk exclusively or have been fed infant
formula containing cow's milk.
(C) In a study of 5,000 infants who were fed only
infant formula containing cow's milk, over
4,000 of the infants never displayed any
symptoms of colic.
(D) When mothers of infants that are fed only breast
milk eliminate cow's milk and all products made
from cow's milk from their own diets, any colic
symptoms that their infants have manifested
quickly disappear.
(E) Infants that are fed breast milk develop mature
digestive systems at an earlier age than do those
that are fed infant formulas, and infants with
mature digestive systems are better able to
tolerate certain proteins and antibodies found in
cow's milk.