Detailed Instructions: 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'.
Problem:Question: Epidemiology allows early detection of changes in the incidence of a certain disease in the population. For this, the most correct thing is to use: 
 Options:  <1> The etiological investigation. <2> The description of the natural history of the disease. <3> Epidemiological surveillance. <4> The evaluation of the functioning of the services. <5> None of the previous answers is correct.
Solution:
3