This is called judicial review.
It's C
The north had the money, the people, and the industrial power to branch out the railroad networks. So following markets and money. The north built networks to the west.
The south in contrast was did not have the capacity to construct as much railroads as the north did so therefore there was less western expansion. As well the south had more interests building canals and shipping product of the states to England.
Scarcity is the fundamental problem facing all societies. It is the condition that results from society not having enough resources to produce all the things that people would like to have.
In order to truly understand an event - whether personal or historical - it is necessary to look at it from multiple perspectives.
Just like you cannot understand history from just one book, you need to ask multiple persons to help you with your personal event.
Answer:
increased number of workers