"As elevation increases, air pressure decreases." could be a good claim. for evidence you could put" when the elevation was 33 feet in ny, the air pressure was 29.92, when the elevation was 594 in chicago, the airpressurewas 29.87, the elevation increased from ny to chicago whil air pressure decreased." for reasoning you could put "The elevation in new york was 33 feet, and the elevation in chicago is greater(594). The air pressure in new york is 29.92, an the air pressure in chicago is 29.87. 29.87 is less than 29.92, therefore the air pressure decreases as elevation increases"or something of that sort. hope this helps!
