(a) Heart is the organ in the human body that acts as a double pump. Hence, organ A represents the heart.
(i) The oxygenated blood from the lungs enters the left atrium (chamber C) via the blood vessel called pulmonary vein (B). Hence, B is pulmonary vein.
(ii) The contraction of left ventricle (chamber D) forces the blood into the blood vessel called aorta (E), which supplies the oxygenated blood to the organs of the body, except the lungs. Hence, E is aorta.
(iii) From the body tissues, the deoxygenated blood is transported back to the heart into the right upper chamber called right atrium (G), by the vena cava (F). Hence, F is vena cava.
(iv) Contraction of chamber G (right atrium) forces the deoxygenated blood into the lower right chamber called right ventricle (H). Finally, the contraction of H (right ventricle), sends the deoxygenated blood into the lungs through the blood vessel called pulmonary artery (I). Hence, I represent pulmonary artery.
(i) The chamber C represents left atrium.
(ii) The chamber D represents left ventricle.
(i) The chamber G represents right atrium.
(ii) The chamber H represents right ventricle.