The Industrial Revolution
Arkansas, Colorado,Louisiana,Montana,New Mexico, North Dakota,Oklahoma,South Dakota, Texas, Utah and Wyoming..
Hope that helps
Answer: D. it lies in a valley, surrounded by mountains, that traps in air pollutants over the city.
Explanation: Being in a valley results in air pollution being contained to an area.
It was the anti-westward movment forbidding all settlers to cross the appalachian mountains.