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
All of the following forces are involved in Antigen antibody reaction except - 
Select and explain. 
A. Vander Waal's forces, B. Electrostatic bond, C. Hydrogen bond, D. Covalent bond
D: Covalent bond
Answer: D: Covalent bond 
Explanation: Antigens are bound to antibodies through weak and noncovalent interactions such as electrostatic interactions, hydrogen bonds, Van der Waals forces, and hydrophobic interactions. Ref: Ananthanarayan & Panikers textbook of microbiology 9th edition pg:103