Ineed to understand about rivalry in north america

Why are constitutions, both federal and state, necessary for our government?

Which was the cause of the rise of the persian empire?

How did the completion of the transcontinental railroad change the lives of american citizens? a-it increased the wealth of all americans and enabled them to travel more. b-it made cross-country travel too expensive for ordinary americans. c-it decreased the safety of americans who moved to settle the plains. d-it shortened travel time between the east and west for all americans.