Based on the plot of oxygen saturation versus partial pressure of oxygen,which of the following statements is true?

A)at oxygen pressure >100 mm Hg,hemoglobin dissociates into individual subunits so that it is able to bind oxygen similar to myoglobin
B)at typical resting capillary oxygen pressure of ~30 mm Hg,hemoglobin has only 1 of its 4 oxygen binding sites filled while myoglobin is nearly saturated with oxygen
C)under periods of extreme muscle exertion,capillary oxygen pressure can drop to 10 mm Hg,allowing release of ~90% of oxygen carried by hemoglobin
D)the structure of hemoglobin allows for complete release of oxygen in capillary beds at all times
E)none of the above