Tourists walk on a path on the Nianjia Lake at Hunan Martyrs Park in Changsha, capital of central China's Hunan Province, Dec. 10, 2019. (Xinhua/Chen Zeguo)

Aerial photo taken on Dec. 10, 2019 shows a bridge over the Nianjia Lake at Hunan Martyrs Park in Changsha, capital of central China's Hunan Province. (Xinhua/Chen Zeguo)

Aerial photo taken on Dec. 10, 2019 shows a boat sailing past a walking path on the Nianjia Lake at Hunan Martyrs Park in Changsha, capital of central China's Hunan Province. (Xinhua/Chen Zeguo)

Aerial photo taken on Dec. 10, 2019 shows a walking path on the Nianjia Lake at Hunan Martyrs Park in Changsha, capital of central China's Hunan Province. (Xinhua/Chen Zeguo)

Aerial photo taken on Dec. 10, 2019 shows the scenery of the Nianjia Lake at Hunan Martyrs Park in Changsha, capital of central China's Hunan Province. (Xinhua/Chen Zeguo)

Aerial photo taken on Dec. 10, 2019 shows two boats sailing on the Nianjia Lake at Hunan Martyrs Park in Changsha, capital of central China's Hunan Province. (Xinhua/Chen Zeguo)

Aerial photo taken on Dec. 10, 2019 shows a walking path on the Nianjia Lake at Hunan Martyrs Park in Changsha, capital of central China's Hunan Province. (Xinhua/Chen Zeguo)

Aerial photo taken on Dec. 10, 2019 shows the scenery of Nianjia Lake at Hunan Martyrs Park in Changsha, capital of central China's Hunan Province. (Xinhua/Chen Zeguo)

Aerial photo taken on Dec. 10, 2019 shows the scenery of Nianjia Lake at Hunan Martyrs Park in Changsha, capital of central China's Hunan Province. (Xinhua/Chen Zeguo)

Aerial photo taken on Dec. 10, 2019 shows boats sailing on the Nianjia Lake at Hunan Martyrs Park in Changsha, capital of central China's Hunan Province. (Xinhua/Chen Zeguo)

Aerial photo taken on Dec. 10, 2019 shows boats sailing on the Nianjia Lake at Hunan Martyrs Park in Changsha, capital of central China's Hunan Province. (Xinhua/Chen Zeguo)