The question is incomplete as it does not have the options which are:
A) release from the bone marrow
B.) seeding of secondary lymphoid organs
C) entering the circulation
D) antigen encounter & activation
Answer:
D) antigen encounter & activation
Step-by-step explanation:
The immune response of the body is determined by the immune cells flowing in the blood.
When a type of immune cell called lymphocytes interact with the antigen (foreign body), this induces the activation of the immune response.
A type of lymphocyte which flows in the blood is B-lymphocytes which contain antibodies and binds with antigen produces cytokines like IL-4,5. These cytokines induce the B cells to produce plasma cells and memory cells. The plasma cells produce more B lymphocytes.
Thus, Option-D is correct.