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A gate to Birmingham Community Charter High School is locked with a sign stating that school is closed, after all schools in the vast Los Angeles Unified School District, the nation’s second largest, were ordered closed due to an electronic threat, December 15, 2015 (AP Photo/Danny Moloshok)

A gate to Birmingham Community Charter High School is locked with a sign stating that school is closed, after all schools in the vast Los Angeles Unified School District, the nation's second largest, were ordered closed due to an electronic threat, December 15, 2015 (AP Photo/Danny Moloshok)