You have discovered a new mammal and have studied the hemoglobin isolated from the blood of this uncharacterized animal. A Hill plot of the O2 binding data for the hemoglobin yields a Hill number of 1.0. Which of the following must be true about this unusual hemoglobin? Note: The hemoglobin from this novel mammal is a tetramer. A. O2 only binds to one of the four hemoglobin subunit and the remaining three subunits do not bind O2. B. The binding of the first O2 to this hemoglobin increases the affinity for the binding of the second O2. C. The binding of the first O2 to this hemoglobin decreases the affinity for the binding of the second O2. D. The binding of the first O2 to this hemoglobin has no effect on the affinity for the binding of the second O2. E. ? cannot reach 1.0 for this hemoglobin, even at high O2 pressures.