As a traveler moves from East to West through the state of Texas what changes would they notice in the landscape?

Air pollution: “combustion results in gases such as nitrogen oxides, nitrogen dioxide and particulates. the main causes of air pollution include transport, domestic combustion and industrial processes. pollutants from these sources can cause problems in the immediate vicinity and a distance away.”

A,) cause a & b are equal & both gives 180°

I'm pretty sure it's c. extremely gradual but not 100% sure though.