During a Storytelling, a Teacher Has Her Children Sitting Comfortably

During a storytelling, a teacher has her children sitting comfortably in a semicircle around her. However, as she reads, the children inch closer to her until they form a knot of haphazardly seated kids. What is an effective way to avoid this?

A) Use tape to mark the boundary of a semicircle area where the children must sit.
B) Keep reminding the children every five minutes to stay in a semicircle.
C) Start out having the children sit in a haphazard arrangement.
D) Punish the first child that starts to creep forward.