Regional trade agreements such as NAFTA impact the WTO a. negatively, because they undercut the nondiscrimination principle of the WTO. b. positively, because they extend most-favored-nation status to more nations. c. negatively, because they compete with the WTO for membership, given that nations can belong to only one trade group. d. negatively, because the U.S. and the EU do not have a regional trade agreement between them