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'.
Input: Question: Atenolol is an antihypertensive -antagonist that belongs to the structural family:
Options: <1> Arylethanolamines <2> Quinazolines <3> -Haloalkylamines. <4> Aryloxypropanolamines. <5> 2-Imidazolines.
Output:
4