Marit Bjoergen of Norway changes her skis during ladies' 30km mass start classic of cross-country skiing at the 2018 PyeongChang Winter Olympic Games at Alpensia Cross-Country Skiing Centre, PyeongChang, South Korea, Feb. 25, 2018. Marit Bjoergen won the gold medal in a time of 1:22:17.6. (Xinhua/Li Gang)