It is Oxygen because we breath it out
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."
<span>It means think in terms of the health of the entire planet (globally) and act in accordance to that in your own backyard/town/area </span>
that there was only one ruler instead of multiple ones.
