Answer: They spun slowly at first, then faster and faster, until the force of their motion rocked the tower. My knees buckled, but I held on".
Step-by-step explanation:
Based on the information that's provided in the question, the quotation that'll be most relevant for Stephon to include in his notes to support the idea that William is courageous will be that "They spun slowly at first, then faster and faster, until the force of their motion rocked the tower. My knees buckled, but I held on".
The quotation shows that William is courageous because it shows that he was brave. Despite the fact that his knees buckled, he held on.