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.
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