You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
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'.

Question: A 13-year-old girl is operated on due to Hirschsprung illness at 3 months of age. Which of the following tumors is more likely to be present?
Options: <1> Abdominal neuroblastoma <2> Wilms tumor <3> Mesoblastic nephroma <4> Familial thyroid medullary carcinoma.
Solution: 2
Why? The answer to the given question should be a tumor, therefore Wilms tumor is the correct answer for the given question.

New input: Question: A group of researchers conducted a prospective study to evaluate the efficacy of three alternatives in the treatment of acute otorrhea in children with tympanostomy tubes. Randomized, 76 children received oral amoxicillin-clavulanic acid, 77 received ear drops with hydrocortisone-bacitracinacolistin and other 77 children did not receive any pharmacological treatment, only observation. The main variable was the presence of otorrhea. What kind of study is it?
Options: <1> Cohort study. <2> Post-authorization study of prospective follow-up. <3> Post-authorization study linked to the authorization. <4> Clinical trial <5> Transversal study.
Solution:
4