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': 'All the following forces are involved in antigen antibody reaction except: \nSelect and explain. \nA. Vander waals forces, B. Electrostatic bond, C. Hydrogen bond, D. Covalent bond', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. (d)Combination between antigen and antibody is firm but reversible and is effected by weak intermolecular forces such as Vander waals forces, ionic bonds and hydrogen bonding, not by the firmer Covalent bonds.The firmness of the union is influenced by affinity and avidity.', 'role': 'assistant'}]