This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology Pa 1 (Immune Response, Antigen-Antibody Reactions, Hypersensitivity, Structure of Immune System, Immunodeficiency Disorders), Subject name: Microbiology
Vaccination is based on the principle of 
Select and explain. 
A. Agglutination, B. Phagocytosis, C. Immunologic Memory, D. Clonal Deletion
C: Immunologic Memory
Answer: C: Immunologic Memory 
Explanation: Option 1, 2, 3, 4 - Natural active immunity: It is acquired by natural clinical or subclinical infections. Such natural immunity is longlasting. For example, individuals suffering from smallpox become immune to second attack of the disease. - Aificial active immunity: It is induced in individuals by vaccines. There is a wide range of vaccines available against many microbial pathogens. These may be live vaccines, killed vaccines, or vaccines containing bacterial products. therefore Immunologic Memory is created AGGLUTINATION- type of antigen antibody reaction Phagocytosis- process of engulfment of paicles, micro-organisms by cells Clonal Detection-By contact with self-antigens during development,self-tolerance is developed by clonal deletion