The adaptive immune system uses multiple strategies to generate diversity in our ability to mount responses to a wide array of infectious microorganisms. These strategies include the generation of diverse repertoires of B-cell and T-cell antigen receptors, as well as polymorphism of MHC genes. The polymorphism of MHC genes differs from the diversity of lymphocyte antigen receptors in that:

Correct Answer: D

Rationale: MHC polymorphism varies between individuals ; receptor diversity is clonal within one (A, B, C are incorrect).

Correct Answer: C

Rationale: Clonal selection is the antigen-driven proliferation of specific B and T cells, not involving NK cells, leukocytes, or complement.

Correct Answer: C

Rationale: The figure (assumed) shows an active plasma B cell at part C, as per the text, typically depicted as antibody-producing.

Correct Answer: C

Rationale: T cells (CD4+) recognize MHCII-antigen complexes and help B cells, unlike antigenic shift (viral reassortment), immature DCs (antigen uptake), or soluble proteins.

Correct Answer: C

Rationale: Isotype switching in germinal centers, driven by CD40 and cytokines, is irreversible and not required for IgM.