This combination photo shows people using telephone booths in Macao (top, photo by Bi Yuenian, archived on Sept. 2, 1994) and a local resident recording videos of a light installation show with a smartphone in Macao, south China on Feb. 12, 2016 (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)