Aerial photo taken on April 21, 2018 shows China's research icebreaker Xuelong berthing at a dock in Shanghai, east China. China's research icebreaker Xuelong finished the country's 34th Antarctic expedition and returned to Shanghai on Saturday. The expedition began on Nov. 8, 2017 and covered a voyage of 38,000 nautical miles. (Xinhua/Fang Zhe)