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police in pennsylvania a student fatally shot a principal before killing himself this morning .
 pennsylvania, police in pennsylvania, a student, a principal, himself
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: organization, person, geographical social political, vehicle, location, weapon, facility 
Text: {0} 
Answer:
 pennsylvania, police in pennsylvania, a student, a principal, himself