The correct option is C
a - iii, b - iv, c - i, d - ii
- Naturally acquired active immunity occurs when a person is exposed to a live pathogen and develops a primary immune response. An example is acquired after smallpox infection.
- Naturally acquired passive immunity occurs during pregnancy, in which certain antibodies are passed from the maternal blood into the fetal bloodstream in the form of IgG.
- Artificially acquired active immunity can be induced by a vaccine, a substance that contains antigen. An example of artificial active immunity is building up a resistance to a disease due to immunization.
- Artificially acquired passive immunity is a short-term immunization by the injection of antibodies, such as gamma globulin, that is not produced by the recipient's cells. eg: Antirabies serum,
- So, the correct answer is 'a - iii, b - iv, ci, d - ii'.