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: Physiology
[{'content': 'Gene for Rh antigen is located on chromosome: \nSelect and explain. \nA. 1, B. 19, C. 4, D. 9', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]