Photo taken on April 24, 2019 shows visitors laughing and dancing in the Summer Palace in Beijing, capital of China. (Xinhua/Zhang Haofu)

Photo taken on April 24, 2019 shows flowers in the Summer Palace in Beijing, capital of China. (Xinhua/Zhang Haofu)

Photo taken on April 24, 2019 shows peach flowers in the Summer Palace in Beijing, capital of China. (Xinhua/Zhang Haofu)

Black swans are seen in the Summer Palace in Beijing, capital of China, April 24, 2019. (Xinhua/Zhang Haofu)

Visitors rest in a corridor in the Summer Palace in Beijing, capital of China, April 24, 2019. (Xinhua/Zhang Haofu)

Photo taken on April 24, 2019 shows the Long Corridor, a roofed walkway, in the Summer Palace in Beijing, capital of China. (Xinhua/Zhang Haofu)

Black swans are seen in the Summer Palace in Beijing, capital of China, April 24, 2019. (Xinhua/Zhang Haofu)

Photo taken on April 24, 2019 shows the scenery of Tower of the Fragrance of the Buddha and the Kunming Lake in the Summer Palace in Beijing, capital of China. (Xinhua/Zhang Haofu)

Photo taken on April 24, 2019 shows the rainy scenery of the Summer Palace in Beijing, capital of China. (Xinhua/Zhang Haofu)

A sightseeing boat is seen in the Summer Palace in Beijing, capital of China, April 24, 2019. (Xinhua/Zhang Haofu)