The answer is letter C. It helped prevented droughts
The government was able to come up a certain way in order to prevent another Dust Bowl to occur in the US. They were able to introduce crop rotation and irrigation and soil tillage. These new farming Methods were introduce under the New Deal. The New Deal program was one of the program being implemented by the US government during the Great Depression
The correct anwser would be climate, because the great potato famine is part of the climate, and was a deciding factor as to why they should leave. I hope you find this helpful, and good luck! :P