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: Anatomy
[{'content': '1st carpometacarpal joint is? \nSelect and explain. \nA. Pivot, B. Hinge, C. Ball and Socket, D. Saddle', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Saddle', 'role': 'assistant'}]