This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
[{'content': 'Chemical nature of complement is \nSelect and explain. \nA. Lipid, B. Polysaccharide, C. Lipo polysaccharide, D. Protein', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Complement is a protein in normal human and animal serum activated by antigen-antibody reactions Ref: Textbook of Microbiology Baveja 5th ed Pg 125', 'role': 'assistant'}]