Answer: Blood to tissue fluid.
Step-by-step explanation:
The respiring tissue needs oxygen (as it is carrying out aerobic respiration). Because of this, it oxygen needs to reach this tissue someway, somehow. And this is via the blood.
The blood contains cells called red blood cells. These cells are responsible for delivering oxygen to the rest of the body. When the oxygen inside these cells reaches the part of the body where oxygen is needed, the oxygen will diffuse through the walls of the artery (out of the blood vessel, into the respiring tissue).