Final answer:
The correct answer is 4. 'pulmonary veins; left atrium,' as the pulmonary veins carry oxygen-rich blood from the lungs to the left atrium of the heart, completing the pulmonary circuit before the blood is pumped throughout the body.
Step-by-step explanation:
The oxygenated blood leaves the lungs through the pulmonary veins and returns to the left atrium. Therefore, the correct answer to the multiple choice question is: 4. pulmonary veins; left atrium. After blood picks up oxygen in the lungs, it travels through the pulmonary veins, which are unique because they are the only veins in the body that carry highly oxygenated blood. These veins lead to the left atrium of the heart. Subsequently, the left atrium contracts and pumps the oxygenated blood into the left ventricle, from where it will be distributed throughout the body via the systemic circulation.
The oxygenated blood leaves the lungs through the pulmonary veins; and returns to the left atrium.The correct answer is 'pulmonary veins; left atrium,' as the pulmonary veins carry oxygen-rich blood from the lungs to the left atrium of the heart, completing the pulmonary circuit before the blood is pumped throughout the body.