Blood Flow in Double Circulation

Steps:

• Blood enters the right atrium, then right ventricle for pulmonary circulation to the lungs.
• Oxygenated blood returns to the left atrium, then left ventricle for systemic circulation to the body.
• One complete circuit passes through all four chambers (two atria, two ventricles).
• Two circuits double the passages, totaling eight chambers.

Why C is correct:

• Human double circulation requires blood to pass through four chambers per full body circuit, so two circuits total eight.

Why the others are wrong:

• A: Counts only two chambers, ignoring the full path through both sides of the heart.
• B: Matches one circuit only, not two.
• D: Overcounts by assuming extra passages not in standard circulation.

Final answer: C