In the late 1800s, American cities suffered from serious environmental pollution due to the smokestack emissions from hydroelectric power plants. The correct answer is D.
It would be important because the ways we are using now are not very affective
The reason people immigrate from one country to another is because they might have natural disasters or land and a occupation is hard to find there. So people might just be migrating to find happiness or a better life than what they had.