Austrian President Alexander Van der Bellen (L) looks at Giant panda Fu Feng, Fu Ban and their mother Yang Yang in the snow-covered Panda garden at Zoo Vienna in Vienna, Austria, on Dec. 1, 2018. Austrian President Alexander Van der Bellen visited the panda twins, Fu Feng and Fu Ban, at Zoo Vienna on Saturday to say goodbye as the pandas will return to Sichuan province, the hometown of giant pandas in China on Sunday. (Xinhua/Liu Xiang)

Giant panda Fu Feng and its mother Yang Yang have bamboos in the snow-covered Panda garden at Zoo Vienna in Vienna, Austria, on Dec. 1, 2018. Austrian President Alexander Van der Bellen visited the panda twins, Fu Feng and Fu Ban, at Zoo Vienna on Saturday to say goodbye as the pandas will return to Sichuan province, the hometown of giant pandas in China on Sunday. (Xinhua/Liu Xiang)

Giant panda Fu Feng has bamboos in the snow-covered Panda garden at Zoo Vienna in Vienna, Austria, on Dec. 1, 2018. Austrian President Alexander Van der Bellen visited the panda twins, Fu Feng and Fu Ban, at Zoo Vienna on Saturday to say goodbye as the pandas will return to Sichuan province, the hometown of giant pandas in China on Sunday. (Xinhua/Liu Xiang)

Giant panda Fu Feng and its mother Yang Yang have bamboos in the snow-covered Panda garden at Zoo Vienna in Vienna, Austria, on Dec. 1, 2018. Austrian President Alexander Van der Bellen visited the panda twins, Fu Feng and Fu Ban, at Zoo Vienna on Saturday to say goodbye as the pandas will return to Sichuan province, the hometown of giant pandas in China on Sunday. (Xinhua/Liu Xiang)

Giant panda Fu Feng has bamboos in the snow-covered Panda garden at Zoo Vienna in Vienna, Austria, on Dec. 1, 2018. Austrian President Alexander Van der Bellen visited the panda twins, Fu Feng and Fu Ban, at Zoo Vienna on Saturday to say goodbye as the pandas will return to Sichuan province, the hometown of giant pandas in China on Sunday. (Xinhua/Liu Xiang)

Giant panda Fu Feng has bamboos in the snow-covered Panda garden at Zoo Vienna in Vienna, Austria, on Dec. 1, 2018. Austrian President Alexander Van der Bellen visited the panda twins, Fu Feng and Fu Ban, at Zoo Vienna on Saturday to say goodbye as the pandas will return to Sichuan province, the hometown of giant pandas in China on Sunday. (Xinhua/Liu Xiang)