Which cells are key to immune regulation?

Correct Answer: B

Rationale: T-regulatory cells regulate immunity; cytotoxic T kill, B cells make antibodies, macrophages phagocytose.

Correct Answer: B

Rationale: Memory lymphocytes provide immune memory; neutrophils , macrophages , and eosinophils are innate.

Correct Answer: A

Rationale: Hassall's corpuscles are a distinctive feature of the thymic medulla.

Correct Answer: B

Rationale: Small to medium lymphatic vessels have thin walls to facilitate lymph flow, but diameter and lumen size vary, so not all apply.

Correct Answer: D

Rationale: The spleen is the largest single intra-abdominal lymphatic organ; the liver is larger but not lymphatic.