1. We was skiing in the Alps, when I saw an avalanche. I saw avalanche, while I was skiing in the Alps
2.They was watching the news, when the lights went out. The lights went out, while they was watching the news
3.People was sleeping, when the wildfire arrived. The wildfire arrived, while people was sleeping
4.I was doing this exercise, when the class finished. The class finished, while I was doing exercise
Сделал как мог.