39. The smallest blood vessels which are one-cell thick, are called ________ A.Vena cava B.Arteries C.Veins D.Capillaries
Answer: Option D Solution: A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter, and having a wall one endothelial cell thick. They are the smallest blood vessels in the body: they convey blood between the arterioles and venules.
