Aldolase is a protein found in the brain. In an experiment, subjects

This is a classic correlation vs. causation CR question. And as always, I like to start with a nice, clear restatement of the conclusion:

This is strong, clear causal language: Aldolase causes the increase in cravings for sweetened drinks. And what's the reasoning given in the passage itself? Really, it's just one sentence that leads to the conclusion:


The author assumes that Aldolase is the cause of the cravings for sweetened drinks, but as is often the case in correlation vs. causation questions, we might wonder if the direction of causality could also be reversed. The author says that Aldolase causes the cravings, but why couldn't the consumption of sweetened drinks lead to higher concentrations of Aldolase in the brain instead?

The question is just asking us to strengthen the conclusion ("an increase in the level of Aldolase in the brain is likely to cause an increase in cravings for sweetened drinks.") One way to strengthen the conclusion might be to eliminate the possibility of a "causal reversal": that the sweetened drinks cause the increase in Aldolase in the brain, instead of Aldolase causing an increase in cravings for sweetened drinks. Also notice that we do not need a statement that PROVES that the conclusion is true; rather, we need a statement that SUPPORTS the argument.


Statement (A) is tempting at first! At first glance, it seems it seems to eliminate the "causal reversal" we discussed above. The trouble is, (A) only addresses the link between craving sweetened drinks and choosing those drinks; it does nothing to link Aldolase to the cravings or the consumption of sweetened drinks. And as we'll see in a moment, (D) is a much stronger answer.


The argument discusses the concentration of Aldolase in the brains of subjects, but the amount of sugar in subjects' brains is irrelevant to the argument. We can eliminate (B).

The argument claims that Aldolase in the brain causes subjects to crave sweetened drinks. Whether Aldolase is present in the drinks themselves is irrelevant to the argument. And even if we (improperly!) assume that drinking "the chemical components of Aldolase" leads to increased Aldolase in the brain, then this would work against the argument, since it would suggest that drinking sweetened drinks causes higher levels of Aldolase in the brain. Either way, (C) is gone.


The answer strengthens the argument by eliminating the possibility that the stated causal relationship is reversed: if the subjects had higher concentrations of Aldolase prior to taking the sweetened drinks, then the sweetened drinks cannot be the cause of the higher concentration of Aldolase. This does not PROVE that the conclusion is true, but it certainly supports the argument.


(E) hurts the argument by suggesting that the causal relationship in the conclusion is reversed: if (E) is true, then drinking sweetened drinks would increase Aldolase levels in the brain, instead of the other way around.

So (D) is our answer.