This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'Which of the following part of psychosexual theory operates on the pleasure principle and attempts to obtain pleasure: \nSelect and explain. \nA. Id, B. Ego., C. Superego., D. None.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]