LSAT Explanation PT 20, S1, Q12: It is probably not true that

LSAT Question Stem

Which one of the following, if true, most seriously weakens the argument? 

Logical Reasoning Question Type

This is a Weaken question. 

Correct Answer

The correct answer to this question is D. 

LSAT Question Complete Explanation

The question type for this problem is Weaken, which means we are looking for an answer choice that undermines the conclusion or the relationship between the premises and the conclusion.

The argument in the passage states that 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. The premise supporting this conclusion is that symptoms of colic are often shown by infants that are fed breast milk exclusively. To weaken the argument, we need to find a connection between cow's milk and colic.

Let's analyze the answer choices:

a) A study involving 500 sets of twins has found that if one infant has colic, its twin will probably also have colic.

- This answer choice supports the conclusion by suggesting that genetics, rather than cow's milk, is the cause of 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.

- This answer choice also supports the conclusion by indicating that infancy itself, rather than cow's milk, could be the cause of colic.

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.

- This answer choice supports the conclusion as well, as the majority of infants fed cow's milk did not develop symptoms of colic, suggesting that cow's milk is not the cause.

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.

- This is the correct answer choice. This information shows that there is a connection between cow's milk and colic, as the elimination of cow's milk from the mother's diet led to the disappearance of colic symptoms in their infants. This weakens the conclusion that cow's milk is unrelated to colic.

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.

- This answer choice supports the conclusion by suggesting that an infant's digestive system, rather than cow's milk, is the cause of the development of colic.

In summary, the correct answer choice is (d), as it weakens the argument by showing a connection between cow's milk and colic. The other answer choices support the conclusion or suggest alternative causes for colic, which does not weaken the argument.