Thanks for the question! So recall from the third paragraph that we’re told that rats that are given drugs that enhance serotonin will eat less carbohydrates (reduce carb cravings), whereas rats that are given drugs that interrupt serotonin will eat more carbohydrates and continue to have carb cravings. Then, in the next paragraph, we’re told that the same thing happens to humans.
Now the question asks us what happens if human beings take a drug that inhibits the action of serotonin, or in other words, interrupts serotonin. Well, we know that in that case, people would eat more carbohydrates and continue to have carb cravings. But this is linked to weight gain (see lines 13-14), not weight loss. So (C) is actually the opposite of what we want, and is wrong.
Hope this helps! Feel free to ask any other questions that you might have.
