Ron Nirenberg, chair of Sister Cities International (SCI) and mayor of San Antonio of Texas, delivers a speech to the fourth U.S.-China Sister Cities Mayors' Summit in Houston, Texas, the United States on July 17, 2019. Representatives from China and the United States are meeting here Wednesday to explore ways to further mayors' cooperation as well as celebrate 40 years of diplomatic ties between the two nations. Themed "40 Years Ahead: Stronger Friendship, Closer Cooperation," the U.S.-China Sister Cities Mayors' Summit has gathered some 200 representatives from dozens of Chinese and U.S. cities and provinces to discuss topics such as innovation and smart cities, maritime silk road, metroplex collaboration and Sino-foreign education exchanges. (Xinhua/Liu Liwei)