CAT Critical Reasoning Practice question with Solution 77

The key to this question is the phrase “in this respect.” We’re told that carbohydrates increase the brain’s level of serotonin, and that “in this respect” carbohydrates act on the brain in the same way as antidepressants. Critical reading tells us that the “respect” in question must be the increase in serotonin—the way the sentence is structured, the author simply can’t be referring to anything else. And that leads right to the correct inference in (D): Some antidepressants must also boost the brain’s level of serotonin.

(A) introduces a false contrast. The stimulus never compares seasonal depression to any other types of depression.

(B) We know that lack of sunlight can cause seasonal depression. We also know that an increase in serotonin can cheer people up. But we cannot combine these facts to conclude that there’s any connection between lack of sunlight and serotonin—the stimulus doesn’t specify why a lack of sunlight is depressing; it may have nothing to do with serotonin.

(C), like (A), offers another comparison that the stimulus simply doesn’t address: The stimulus never compares midwinter to any other season. There may be other times of the year when other causes, more serious than a lack of sunlight, make more people depressed.

(E) attempts to slip a scope shift by us: Serotonin is the only neurotransmitter mentioned in the passage that has the stated effect on depression; (E) tries to extend the argument to include all neurotransmitters. There’s no basis for that—for all we know, some neurotransmitters may even have a depressing effect.