This combination photo shows the construction site of Macao International Airport (top, photo by Bi Yuenian, archived on Sept. 6, 1993) and people visiting the 2019 Macao Business Aviation Exhibition at Macao International Airport in Macao, south China on Nov. 1, 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)