The school Principal received several complaints from parents about bullying on the school campus during recess. He wants to investigate the matter and find the culprit. Therefore, he instructs one of his teachers to look after the students during recess. Which situation should the teacher report to the Principal? (A) A lonely girl is sitting under the tree and crying. (B) Four boys are forcefully trying to open another boy's backpack. (C) Five girls are playing catch-and-throw game. (D) Three boys are huddled over a mobile phone which is not supposed to be on-school campus.