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: Which of the following is the central characteristic of the stage of formal operations according to Piaget ?: 
 Options:  <1> The solution of conservation problems. <2> The reversibility in thought. <3> The overcoming of egocentrism. <4> The theory of the mind <5> The hypothetical-deductive thought.
