Which of the Following Statements About O₂-Binding Curves Is False

Which of the following statements about O₂-binding curves is false?

A) A smaller decrease in P_O2 is needed for hemoglobin to drop from 100 percent to 75 percent saturation than for hemoglobin to drop from 75 percent to 50 percent saturation.
B) In normal metabolism, the body uses only the upper one-fourth of its oxygen-binding curve.
C) The blood normally carries an enormous reserve of O₂.
D) The steepest part of the O₂-binding curve results in a great release of O₂ for only a modest drop in P_O2.
E) The P_O2 of blood drops below about 40 mm Hg only during extreme exertion.