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': 'Rh factor is a: \nSelect and explain. \nA. Antibody, B. Mucopolysaccharide, C. Lipoprotein, D. Glycoprotein', 'role': 'user'}, {'content': "Answer: A \nExplanation: A Rheumatoid factor is an antibody (auto-antibody) of any immunoglobulin class directed against a specific region of the Fc fragment of human IgG. Ref: Harrison's Principles of Internal Medicine, 17th Edition, Page 2155; Davidson's Principles and Practice of Medicine, 20th Edition, Page 1074", 'role': 'assistant'}]