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: Microbiology
[{'content': 'Rheumatoid factors are immunoglobulins directed against: \nSelect and explain. \nA. The Fc poion of immunoglobulin G (IgG), B. The Fc poion of immunoglobulin A (IgA), C. The Fc poion of immunoglobulin M (IgM), D. The Fc poion of immunoglobulin D (IgD)', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The Fc poion of immunoglobulin G (IgG)', 'role': 'assistant'}]