In the following figure, which answer is correct?

Correct Answer: C

Rationale: T-lymphocytes enter lymph nodes via post-capillary venules ; figure context suggests lymph node, not tonsil , spleen , or efferent entry .

Correct Answer: A

Rationale: NK cells produce cytokines and release cytotoxic chemicals ; they detect missing MHC I (C indirectly), not general traits , and activate macrophages secondarily.

Correct Answer: C

Rationale: B7 binds CD28 for T-cell co-stimulation ; not TCR-nucleus , adhesion , or upregulation .

Correct Answer: C

Rationale: Mucus acts as a barrier with antimicrobial proteins ; protection is broader, SCFAs are microbiota-derived, not nutrient transport .

Correct Answer: D

Rationale: Mesenteric nodes are deep in the abdomen, not palpable; axillary , inguinal , and cervical are superficial.