Aerial photo taken on April 10, 2020 shows the spring scenery of the Mutianyu Great Wall in Beijing, capital of China. (Xinhua/Zhang Chenlin)

Aerial photo taken on April 10, 2020 shows the spring scenery of the Mutianyu Great Wall in Beijing, capital of China. (Xinhua/Zhang Chenlin)

Aerial photo taken on April 10, 2020 shows the spring scenery of the Mutianyu Great Wall in Beijing, capital of China. (Xinhua/Zhang Chenlin)

Aerial photo taken on April 10, 2020 shows the spring scenery of the Mutianyu Great Wall in Beijing, capital of China. (Xinhua/Zhang Chenlin)

Photo taken on April 10, 2020 shows the spring scenery of the Mutianyu Great Wall in Beijing, capital of China. (Xinhua/Ju Huanzong)

Photo taken on April 10, 2020 shows the spring scenery of the Mutianyu Great Wall in Beijing, capital of China. (Xinhua/Ju Huanzong)

Photo taken on April 10, 2020 shows the spring scenery of the Mutianyu Great Wall in Beijing, capital of China. (Xinhua/Ju Huanzong)

Photo taken on April 10, 2020 shows the spring scenery of the Mutianyu Great Wall in Beijing, capital of China. (Xinhua/Ju Huanzong)