This combination photo shows an aerial view of the Ruins of St. Paul's complex and its surroundings in Macao, south China (top, photo by Chen Demu, archived on Nov. 7, 1986) and an aerial view of the same area on Oct. 24, 2019 (bottom, photo by Cheong Kam Ka). On Dec. 20, Macao will celebrate the 20th anniversary of its return to motherland. Over the past two decades, the special administrative region has made great strides in economic development and achieved prosperity and stability under the "one country, two systems" principle. Since Dec. 20, 1999, the historic day for Macao, what has changed? And what remains unchanged? Our selection of photos present comparative illustrations of the south China city's past and present. (Xinhua)