This combination photo shows an aerial view of the Macao Peninsula in south China (top, photo by Bi Yuenian, issued on Aug. 15, 1992) and an aerial view of Macao, south China on Nov. 18, 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)