Which organ is key to B cell activation?

Correct Answer: C

Rationale: Lymph nodes activate B cells; thymus matures T cells, spleen filters, marrow produces.

Correct Answer: D

Rationale: Bicuspid valves in lymphatic vessels ensure unidirectional lymph flow; tricuspid, aortic, and pulmonary valves are in the heart.

Correct Answer: C

Rationale: The spleen's capsule contains vessels, nerves, muscle , dense C.T. , and trabeculae ; it's thick at the hilum, not thin (C is incorrect).

Correct Answer: B

Rationale: Thymus is located in the thoracic cavity behind the sternum.

Correct Answer: D

Rationale: Spleen destroys RBCs , stores blood/platelets , forms fetal blood ; lymph filtration is a lymph node function .