A reduction in the number of circulating RBCs would cause:

Correct Answer: B

Rationale: Anemia (B) is low RBCs/hemoglobin.

Correct Answer: B

Rationale: Type B (B) has B antigen, anti-A antibodies.

Correct Answer: C

Rationale: Hemocytoblasts (C) are pluripotent stem cells for RBCs.

Correct Answer: D

Rationale: Prothrombinase production (D) drives clotting, not control.

Correct Answer: A

Rationale: Elastic arteries (e.g., aorta) are compliant (A), stretching to accommodate systolic pressure. They don’t reduce flow (B), aren’t resistance vessels (C, muscular arteries), and have thick, regular walls (not D).