Students have PE class at the Pui Ching Middle School in Macao, south China, March 21, 2019. 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. (Photos: Xinhua/Cheong Kam Ka)

People visit the Ruins of St. Paul's complex in Macao, south China, Dec. 12, 2019. 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.

People pass by the Border Gate in Macao, south China, Dec. 12, 2019. 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.

Aerial photo taken on Oct. 21, 2019 shows a view around the St. Paul's complex and the Mount Fortress in Macao, south China. 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.

Aerial photo taken on Nov. 18, 2019 shows the scenery of Macao Peninsula in south China. 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.

Aerial photo taken on Nov. 10, 2019 shows a view of the Gongbei Port in Zhuhai, south China's Guangdong Province, and the Border Gate in Macao, south China. 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.

A flag-raising ceremony is held at the Hou Kong Middle School in Macao, south China, Nov. 18, 2019. 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.

Aerial photo taken on Nov. 1, 2019 shows the view near Taipa Houses-Museum in Macao, south China. 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.

Aerial photo taken on Oct. 23, 2019 shows the Macao Tower in Macao, south China. 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.

Aerial photo taken on Oct. 20, 2019 shows the new Hengqin Port in Zhuhai, south China's Guangdong Province. 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.

People visit the Golden Lotus Square in Macao, south China, Dec. 13, 2019. 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.