Not have germinal Center, contain high B-lymph, low T lymph.

Correct Answer: A

Rationale: Primary follicles lack germinal centers and are rich in B-lymphocytes, with few T-lymphocytes.

Correct Answer: C

Rationale: Blood-thymic barrier has continuous endothelium and thick basement , protects immature T-cells ; T-lymphocytes are in both cortex and medulla, but immature are in cortex (C is incorrect).

Correct Answer: D

Rationale: Lingual tonsils have ducts opening at crypt bases, reducing inflammation by clearing debris ; location and epithelium don't fully explain (A, B), surface ducts are incorrect .

Correct Answer: C

Rationale: Macrophages engulf pathogens and fuse phagosomes with lysosomes to destroy them ; cytokine production and direct killing are secondary roles.

Correct Answer: A

Rationale: APCs (antigen-presenting cells) activate T cells ; killing and antibody production are other cell roles, not repair .