Simple.....
First off what does NAFTA even mean?
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North American Free Trade Agreement
Withing this Agreement is Canada, Mexico, and the United States.
B is out of the question...along with C.
The purpose of NAFTA was to eliminate taxes within all products shipped through Canada all the way down to Mexico.
This being said...the purpose of NAFTA was to facilitate the cross-border movement of goods and services.
Thus, your answer.