When Mexico became a part of NAFTA, along with Canada and the United States, it:
选项：

A:Eliminated traiffs against Canada and the United States but maintained them against nonmembers
B: Eliminated traiffs against Canada, the United States, and all nonmember countries
C: Increasedtraiffs against Canada the United States, and all nonmember countries
D: Increased traiffs against Canada and the United States, but did not change them against nonmember countries