This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Mood disorders, Subject name: Psychiatry
[{'content': 'Most common psychiatric illness \nSelect and explain. \nA. Depression, B. Bipolar, C. Mania, D. Cyclothymia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Mood disorders are common. In the most recent surveys, major depressive disorder has the highest lifetime prevalence (almost 17 percent) of any psychiatric disorder. Reference: Synopsis of Psychiatry, page 348.', 'role': 'assistant'}]