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: What is the most frequent etiology of aortic stenosis in adults? 
 Options:  <1> Rheumatic <2> Congenital <3> Degenerative or calcified <4> Post endocarditis. <5> Ischemic
