Input (grade 13): The Columbine High School massacre occurred on Tuesday, April 20, 1999, at Columbine High School in Columbine, an unincorporated area in Jefferson County, Colorado, United States, near Denver and Littleton.
Output (grade 7): The Columbine High School Massacre was a murder/suicide at Columbine High School near Denver, Colorado on April 20, 1999.