When You Are Lying on the Couch, Resting, the Blood

When you are lying on the couch, resting, the blood going from your heart to your lungs is approximately _______ % saturated with oxygen.When you are running fast on a treadmill, _______.

A) 0; your active muscles extract most of the oxygen bound to hemoglobin
B) 25; your active muscles extract all the oxygen that is bound to hemoglobin
C) 50; the partial pressure of oxygen in your active muscles is high, causing most bound oxygen to be released from hemoglobin in these tissues
D) 75; the lower partial pressure of oxygen in your active muscles causes hemoglobin to release more bound oxygen to these tissues
E) 100; the partial pressure of oxygen in your blood falls below 40 mm Hg