In Which One of the Following Situations Would It Be

In which one of the following situations would it be best to ignore a student's behavior?

A) Fritz and Irene are throwing paper airplanes across the room at each other.
B) Jim keeps pulling Jackie's hair while she is trying to work at her desk.
C) Harriet gets up to sharpen her pencil at least once every ten minutes.
D) Mary asks a classmate to clarify an assignment and then returns to her work.