BEIJING, Sept. 22 (Xinhua) -- As Chinese President Xi Jinping prepares to pay a state visit to the United States, trade and economic issues are an inevitable topic of his talks with U.S. President Donald Trump. Economic and trade relations should continue to serve as the "ballast" and driving force for China-U.S. relations, rather than a stumbling block or a point of friction, Xi told Trump in Busan, South Korea