世界貿易組織 關稅暨貿易總協定 關稅暨貿易總協定 第二十四條之區域貿易協定 北美自由貿易協定 歐盟 最惠國待遇 World trade organization WTO General agreement on tariffs and trade GATT General agreement on tariffs and trade GATT Regional trade agreements RTAs North American free trade agreement NAFTA European Union EU Most-favored-nation treatment MFN