Happy to help. You ask why Answer B is incorrect. Answer B describes a causal relationship - lack of sunlight lowers the level of serotonin in the brain. Can that be properly inferred from the passage? Let’s take a look.
The passage describes a few causal relationships. Lack of sunlight causes seasonal depression. Carbs cause increase in serotonin. Increase in serotonin improves mood. In this respect, carbs act like antidepressants. What can we infer from these statements?
Answer B says a lack of sunlight lowers the level of serotonin in the brain. We know the increased levels of serotonin improves mood, but the passage does not describe the brain chemistry that causes seasonal depression. Perhaps there is another neurotransmitter at play. Just because boosting serotonin is the remedy for seasonal depression doesn’t necessarily mean that low levels of it are what cause it. Therefore it cannot be properly inferred that low sunlight lowers serotonin.
Answer D is the correct choice. It says that some antidepressants act by changing the brain’s level of serotonin. This can be properly inferred because the passage says that carbs improve mood by increasing levels of serotonin and “in this respect, carbohydrates act on the brain in the same way as some antidepressants.†Because the passage explicitly says that carbs work in the same way as some antidepressants, we can apply what the passage tells us about how carbs work to antidepressant medication.
I hope this is helpful! Please reach out with other questions!
