The correct answer is option D. 5 (lung capillaries).
Explanation:
The oxygen first enters in lung capillaries into the bloodstream from the alveoli by the simple diffusion. There is a network of tiny vessels known as capillaries from the alveoli sacs of lungs.
Lung capillaries transport the oxygenated blood to the heart and from there it pumps to the different parts of the body where blood carries the carbon dioxide in veins to the heart.
Thus, the correct answer is option D. 5. (lung capillaries).
