I believe your answer is B
Answer: D. construction and protection of roads that ensured safe and easy travel
Explanation:
Under Genghis Khan and his descendants, the Mongols conquered much of Asia and some of Eastern Europe such that they created the largest land empire ever seen.
Even though these Mongols could be brutal in conquest, they increased trade in the region by repairing the networks of roads that connected their conquered areas as well as constructing more. The protection they afforded these roads was renowned thus making travel easy.
Because the US had a great geographical location which shileded them from immediate contact with any military force. This was one thing, another thing was that they were lending money to the different European nations which they had to return after some time. All of this enabled the US to catapult itself and become a world power.
The answer is C to overthrow the government and establish a new one