inputs: hypothesis: Nearby are two volcanoes that can only be seen from the city on days when wind has cleared out the pollution. premise: Toward the east , the city ends in a plain that meets the Sierra Nevada , with its two extinct volcanoes, Ixtacihuatl ( 17,342 feet ) and Popocatepetl ( 17,883 feet ), which were once a familiar sight from Mexico City but are now usually obscured by pollution.