This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S., Subject name: Medicine
[{'content': 'Myasthenia gravis may be associated with: \nSelect and explain. \nA. Drug intake, B. Viral infection, C. B lymphocyte dysfunction, D. Thymoma', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans: dRef: Harrison, 16thed, p. 2521, Table 366.3', 'role': 'assistant'}]