Canada is located to the north of the united states. due to its shared border, the us and canada, along with mexico, entered into a trade agreement known as
a) the european union.
b) the united nations.
c) the world trade organization.
d) the north american free trade agreement.

b

explanation:

explanation:

the addition to geographic boundaries that might have  kept the people of the huang river civilization from traveling to far distance region is that they had learned about the other river valley civilizations but feared contact would bring invasion.

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