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a. Capillaries are short vessels with thin walls that create strong pressures forcing gas-infused blood to diffuse to the surrounding tissue.
b. Capillaries have thin walls and narrow diameters so that blood cells come close to the thin walls, across which gases can diffuse to surrounding tissue.
c. Capillaries have valves along their walls that allow blood cells to move through them to surrounding tissue, where gas exchange can occur.
d. Capillaries regulate the pressure of blood within them so that a steady stream of gas-infused blood cells passes into the surrounding tissue.
Use process of elimination.
Capillaries don't have valves along their walls - only veins have that. So it is not the third option. Similarly, capillaries cannot regulate the pressure of blood within them, so it is not the four option either.
Do you have any thoughts about whether it is option one or two?
um afraid i have more chance of giving wrong option