Photo taken on April 28, 2021 shows the scenery of Schonbrunn Gardens in Vienna, Austria. (Xinhua/Guo Chen)

Photo taken on April 28, 2021 shows the scenery of Schonbrunn Gardens in Vienna, Austria. (Xinhua/Guo Chen)

Photo taken on April 28, 2021 shows the scenery of Schonbrunn Gardens in Vienna, Austria. (Xinhua/Guo Chen)

Photo taken on April 28, 2021 shows the scenery of Schonbrunn Gardens in Vienna, Austria. (Xinhua/Guo Chen)

Photo taken on April 28, 2021 shows the scenery of Schonbrunn Gardens in Vienna, Austria. (Xinhua/Guo Chen)

Photo taken on April 28, 2021 shows the scenery of Schonbrunn Gardens in Vienna, Austria. (Xinhua/Guo Chen)

Photo taken on April 28, 2021 shows the scenery of Schonbrunn Gardens in Vienna, Austria. (Xinhua/Guo Chen)

Photo taken on April 28, 2021 shows the scenery of Schonbrunn Gardens in Vienna, Austria. (Xinhua/Guo Chen)

Photo taken on April 28, 2021 shows the scenery of Schonbrunn Gardens in Vienna, Austria. (Xinhua/Guo Chen)