Answer: B) an increase in free trade between Canada and United States and Mexico.
Step-by-step explanation:
Since the signing of the North American Free Trade Agreement (NAFTA) in 1993, trade has substantially increased between the United States, Canada and Mexico.
This much is proven by the graph where we see that each of the three countries have seen a yearly increase in the amount of goods supplied to the others which points to large trading activities between all three countries.