BEIJING Chinese Vice Commerce Minister Wang Shouwen has told his U.S. counterpart that a modern China was an economic "opportunity" not a "threat" to the United States. Trade is one of the many areas of friction between the world's two leading powers, along with rivalry in technology and tensions in the South China Sea and over Taiwan. Wang met U.S. Under Secretary of Commerce for International Trade Marisa Lago in the northern port city of Tianjin, the second meeting this year between the two