Oxygen Moves from Blood into the Interstitial Fluid and Then

Oxygen moves from blood into the interstitial fluid and then to body cells because

A) it diffuses from a region of higher partial pressure to a region of lower partial pressure.
B) it diffuses from a region of lower partial pressure to a region of higher partial pressure.
C) it descends down an osmotic gradient, following the movement of water.
D) it diffuses from a higher to a lower pH.