B. Birds of a feather flock together.
Hi,
The answer to your question is "Equity Theory"
Answer:
This began the Middle Kingdom and a new period of stability, which lasted from 2055 to 1650 B.C.E. The Middle Kingdom has been labeled by historians as a the Golden Age due to the economic, social and political stability of the time period. Trading, arts and literature all flourished in the Middle Kingdom.
Explanation:
I think that railroads helped because people could get their goods faster and people could send out more goods across America.
Your answer would be D.
I logic this out in this way:
Exchanging currencies wouldn't be of much use unless you plan to buy something from a country that uses that currency.
Hope this helps.