Question

the narrowest blood vessels are called: a arterioles. b veins. c capillaries. d venules.

Explanation:

Capillaries are the smallest and narrowest blood vessels in the body, enabling the exchange of substances between blood and tissues. Arterioles are small arteries, veins carry blood back to the heart, and venules are small veins. Capillaries have a single - cell - thick wall which is ideal for diffusion processes.

Answer:

C. capillaries