Which of the following choices best explains why the author cannot say for certain how romantic love affects levels of serotonin in the brain? Answer choices for the above question A. There has not been a purely neurological study examining the relationship between the two. B. Some evidence suggests that romantic love increases serotonin and other evidence suggests it decreases serotonin. C. Serotonin does not have strong effects on the brain compared to dopamine and norepinephrine. D. There is a possibility that study subjects were not actually in love, but rather just suffering from obsessive-compulsive disorder.