Tourists view the Zhaozhou Bridge, the oldest standing stone-arched bridge in China, across the Xiaohe River in Zhaoxian County, north China's Hebei Province, April 5, 2019. (Xinhua/Liang Zidong)

Tourists visit the Summer Palace on the second day of a three-day Qingming Festival national holiday in Beijing, capital of China, April 6, 2019. (Xinhua/Li Xin)

Tourists visit the Summer Palace on the second day of a three-day Qingming Festival national holiday in Beijing, capital of China, April 6, 2019. (Xinhua/Li Xin)

Tourists pose for a selfie amid cole flowers on the second day of a three-day Qingming Festival national holiday in Donggequan Village of Shahe, north China's Hebei Province, April 6, 2019. (Xinhua/Chen Lei)

Tourists visit the Summer Palace on the second day of a three-day Qingming Festival national holiday in Beijing, capital of China, April 6, 2019. (Xinhua/Li Xin)