Photo taken on Feb. 12, 2020 shows the blooming tulips at a tulip exhibition in San Francisco, the United States. (Photo by Li Jianguo/Xinhua)

Photo taken on Feb. 12, 2020 shows the blooming tulips at a tulip exhibition in San Francisco, the United States. (Photo by Li Jianguo/Xinhua)

Photo taken on Feb. 12, 2020 shows the blooming tulips at a tulip exhibition in San Francisco, the United States. (Photo by Li Jianguo/Xinhua)

A visitor takes photos of the blooming tulips at a tulip exhibition in San Francisco, the United States, Feb. 12, 2020. (Photo by Li Jianguo/Xinhua)

Photo taken on Feb. 12, 2020 shows the blooming tulips at a tulip exhibition in San Francisco, the United States. (Photo by Li Jianguo/Xinhua)

A visitor takes photos of the blooming tulips at a tulip exhibition in San Francisco, the United States, Feb. 12, 2020. (Photo by Li Jianguo/Xinhua)

Photo taken on Feb. 12, 2020 shows the blooming tulips at a tulip exhibition in San Francisco, the United States. (Photo by Li Jianguo/Xinhua)

Photo taken on Feb. 12, 2020 shows the blooming tulips at a tulip exhibition in San Francisco, the United States. (Photo by Li Jianguo/Xinhua)