At least 20 students were injured with stab wounds,some life threatening, on Wednesday at a high school near Pittsburgh, Pennsylvania,and a suspect was arrested, police reported.Four people were flown to hospitals by helicopter after the stabbings at FranklinRegional Senior High School, officials said.The stabbings happened in classrooms and hallways, and the victims ranged in agefrom 14 to 17, officials said.The school is in Murrysville, about 15 miles east of Pittsburgh.