Which of the following is true about veins ?

Correct option is D

The correct answer is (d).
Explanation
Veins carry blood back to the heart and contain valves that prevent the backward flow of blood. These valves are essential because blood in veins often flows against gravity, especially from the lower parts of the body.
Additional Information
• Option {a} is incorrect because veins generally carry deoxygenated blood, except the pulmonary vein. • Option {b} is incorrect because arteries carry blood from the heart to different parts of the body. • Option {c} is incorrect because veins have thinner walls compared to arteries.