It's called a "city-state"
The best option will be the C. Railroads made the rapid movement of produce and goods into many markets possible.
Because Railroads basically were the key point to national business and economic growth. Eliminating the needs for long and weary trips, while also founding and fueling other soon-to-be huge business industries, such as iron, coal, copper, machinery, etc., railroads made "rapid movement of produce and goods into many markets possible."
