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: Pathology
[{'content': 'Swift disease occurs due to: \nSelect and explain. \nA. Mercury., B. Lead., C. Bismuth., D. Arsenic.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]