Diagram

There actually isn't a need for a diagram here. Let's break this argument down. This is a Must Be True question, so our correct answer will be 100% supported by the passage. Conclusion: "eating holiday cookies may provide an effective form of self prescribed medication." Why? We are given the theory that baking for winter holidays is a tradition that could have actual medical roots. We know that when the days are shorter, in midwinter, some people suffer from a certain type of seasonal depression caused by lack of sunlight. We are told that "carbohydrates, both sugars and starches, boost the brain's levels of serotonin, a neurotransmitter that improves the mood. In this respect, carbohydrates act on the brain in the same way as some antidepressants." We are told that carbohydrates boost the brain's level of serotonin, and, in doing so, they "act on the brain in the same way as some antidepressants." Therefore, it must be true that some antidepressant act in this way, i.e. boost the brain's level of serotonin. Answer choice (D) states: "Some antidepressants act by changing the brain's level of serotonin." This is what we have inferred above. It is 100% supported by the passage. Hope that helped! Please let us know if you have any more questions.

Why isn't E true?

The problem with (E) is that it is not 100% supported. Improving one's mood is NOT the same thing as "effectively relieves depression." Hope that helps! Please let us know if you have any other questions.

Why is B not true? It is what the entire passage depends on!

I could see why all of them but E are true. Can you explain why A, B, and C don't work? I see how D does work as well, I just want to know what we're looking for to completely exclude A, B, and C. Thanks in advance!

@Ceci this is a Must Be True question so if you are picking an answer choice, you should be able to point to the part of the stimulus that directly supports the answer you are choosing. For example, (D) is directly supported by the following sentences in the stimulus: "Carbohydrates, both sugars and starches, boost the brain's levels of serotonin, a neurotransmitter that improves the mood. In this respect, carbohydrates act on the brain in the same way as some antidepressants." If you think (A), (B) or (C) can also work, can you please identify the part of the stimulus that directly supports each of these answer choices?