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