Definition: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Input: Question: If the arterial pO2 decreases to 60 mm of Hg:
Options: <1> Decreases ventilation. <2> Central chemoreceptors are activated. <3> The central chemoreceptors are depressed. <4> The arterial chemoreceptors are activated. <5> It produces loss of consciousness.
Output:
4