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': "Fredrich's ataxia is caused by which type of mutation - \nSelect and explain. \nA. Point mutation, B. Expanded trinucleotide repeat, C. Missense mutation, D. Inversion", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]