Task: Question Answering
Input (English): Question: Which of the following conditions causes a decrease in the O2 saturation of the hemoglobin that is not due to a decrease in the partial pressure of oxygen? 
 Options:  <1> Ventilation-perfusion ratio lower than normal. <2> Anemia. <3> Carbon monoxide poisoning. <4> Hypoventilation. <5> Shunt venoarterial.
Output (English): 3