What are the reasons for the several day delay in a primary response. a. transport to secondary lymphoid tissue b. antigen processing and presentation c. small initial # of lymphocytes specific for the antigen d. proliferation and differentiation.

The correct answer is D. proliferation and differentiation.

Explanation:

Primary immune response occurs due to the first exposure of an antigen to the immune system. The primary immune response is generally delayed by many days because it takes time for B and T cells to become cloned and to proliferate and differentiate.

Then after several days of proliferation and differentiation of activated T and B cells, T cells become effector T cells and B cell becomes plasma cells which then eliminates the antigen. Memory B and T cells are also produced during this process which helps in generating a quick immune response during the second and subsequent exposure of that antigen.

So the correct answer is D. proliferation and differentiation.

a = executive branch; b = judicial branch