<p>bully </p>
<p>Explanation:</p>
<p>I will catch one of the five girls who bullies/bully(me) in class.</p>
<p>‘‘who bullies/bully(me) in class’’ is an adjectival restrictive clause that modifies girls(which girls??). Who is the subject of that clause, and who’s antecedent is ‘‘girls’’.Thus, who acts as a plural noun.</p>