<prompt> Which of the following ranges of hemoglobin O2 saturation from systemic venous to systemic arterial blood represents a normal resting condition?25 to 7540 to 7540 to 9575 to 98  <response>: Ans. D. 75 to 98In a normal resting condition, the blood leaving the lungs is 98 saturated with oxygen, and the blood returning to the lungs is 75 saturated with oxygen. With vigorous exercise, blood leaving the lungs is still 98 saturated, but blood returning is usually less than 75 saturated because more oxygen is unloaded from hemoglobin in exercising muscles. 