25 POINTS!!!!!!!!!!
Which of the following gradients allow oxygen to leave the blood and enter body tissues and carbon dioxide to leave body tissues and enter the blood?

A. High concentration of oxygen in the blood; high concentration of carbon dioxide in the body tissues
B. Low concentration of oxygen in the blood; high concentration of carbon dioxide in the body tissues
C. High concentration of oxygen in the blood; low concentration of carbon dioxide in the body tissues
D. Low concentration of oxygen in the blood; low concentration of carbon dioxide in the body tissues