Your understanding of the word claim is still askew. Hint: A citation is not the same as a claim, these are simple concepts that you can grasp if you try your hardest.
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Please make use of your Google-fu if you would care to explore Ms. Jacobs research and reporting. It is really quite easy but if you are unable please find someone to instruct you.
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Now answer the question.
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Is it your contention that mass murderers are mentally healthy and emotionally stable? If so, please "confirm your own claim."
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Mentally disturbed individuals might use jet aircraft, car bombs or pressure cookers to commit mass murder.
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Please have someone explain the word "might" to you also, as your understanding of that particular verb seems to be eluding you.