Question

"What was the primary cause of the trends shown on the graph?

(1)closing of the western frontier
(2)industrialization in the North and the Midwest
(3)passage of the Homestead Act
(4)completion of the transcontinental railroad"

Answer 1

I think the most suitable options are (1)closing of the western frontier or (2)industrialization in the North and the Midwest. I think, I'd go with second one.