One student was killed and 23 others were injured when a bus packed with Long Beach high school students on a ski trip flipped on its side on an icy highway about 75 miles south of Salt Lake City. Christin Baker, a 17-year-old cheerleader and honor student, was crushed to death after she was thrown from the chartered Greyhound bus and it rolled on top of her, a Utah Highway Patrol spokeswoman said. The bus was filled with more than 40 youths from Wilson High School in Long Beach on an Explorer Scout-sponsored trip to Sun Valley, Ida. Karen Rossebo, 17, was listed in serious condition at Utah Valley Regional Medical Center in Provo with a crushed pelvis and broken legs. Four other youths were being held overnight for observation at two other area hospitals. The remainder of the teen-agers were treated for bruises and released.