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the study also found more than half the students who perpetrated attacks were motivated by revenge and had a history of gun use .
 more than half the students who perpetrated attacks, who, gun
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: geographical social political, organization, person, location, facility, vehicle, weapon 
Text: {0} 
Answer:
 more than half the students who perpetrated attacks, who, gun