Which of the following statements does not apply to the k value in the equation for the oxygen binding curve of myoglobin? a) it is numerically equal to p50. b) it is defined as that oxygen partial pressure at which half of the oxygen binding sites are occupied. c) it is a measure of the affinity of myoglobin for oxygen. d) if y > k, then myoglobin is less than 50% saturated with oxygen. e) it is the value of po2 at which y = 0.5.