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: Medicine
[{'content': 'Gene for myotonic dystrophy is coded on chromosome number - \nSelect and explain. \nA. 19, B. 20, C. 21, D. 24', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]