Answer: A
Explanation:
they used astronmy to to develop calendars based based on the movement of stars and planets. B, C, and D are incorrect.
I believe the answer is A but i could be wrong, during the Civil war it made it easier for them to speak and talk to each other during that time sending goods and messages across the united states.
Hope this helps.
Answer:
d.china/ huang he river valley
Explanation:
When the Monroe Doctrine was written, the US had just formed and was not ready to fight the European powers. Monroe basically asked Europe to stay out of the Western Hemisphere because they were afraid of getting attacked.
The creator, James Monroe, was interested in keeping the United States out of a war it was not prepared for. Though it was out of fear, there was some thinking through; people voted on it, after all.
Note that by "afraid of getting attacked," I not only mean getting attacked through soldiers and cannons but also by taking over nearby areas and competing with the US for natural resources.
4 years, let me know if it is right.