Which of the Following Statements About the Binding of Oxygen

Which of the following statements about the binding of oxygen by hemoglobin is false?

A) The percentage of completely O₂-saturated hemoglobin increases as P_O2 increases.
B) The oxygen-binding curve is S-shaped.
C) There is a narrow range of the O₂-binding curve where O₂ dissociation-association is rapid.
D) A very low P_O2 is required for all four hemoglobin subunits to bind to O₂.
E) If one subunit of a completely oxygen-saturated hemoglobin loses its O₂, the affinity of the remaining subunits for their O₂ increases.