<prompt>  Which of the following is true to the immediate postoperative period in a young patient with previously normal lungs having upper abdominal surgery ?Arterial oxygen tension will typically be reduced by an average of 10 mm Hg when breathing room airArterial oxygen tension will normalize after 15 minutesDiffusion hypoxia is the major determinant of arterial hypoxaemiaThe CXR will typically reveal no abnormalities 