U.S. Federal Reserve chair Janet Yellen speaks during her testimony before the Joint Economic Committee of the U.S. Congress on Capitol in Washington D.C., capital of the United States, on Nov. 17, 2016. Yellen said on Thursday that it will be appropriate for the central bank to hike interest rate relatively soon, and warned of the risks of keeping rate low for too long. (Xinhua/Yin Bogu)