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<p>Alright. Seems reasonable enough. Who does not refer to the three people, it refers to Jason. Hence, if we omit “of the three people I knew well in middle school”, the sentence would no longer be correct due to faulty noun-verb agreement. OK then.</p>
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<p>Let me just restate the obvious. What is who referring? Obviously, who does not refer to one. Why? Because if we omit “of the five girls”, the sentence makes no sense -> I will catch one who bullies me in class? So in this case, who refers to the five girls, which makes the sentence more comprehensible and consistent. Am I correct?</p>