Harriett Goes Trick-Or-Treating on Halloween

Harriett goes trick-or-treating on Halloween.She arrives at her neighbour's door just as the phone is ringing.Her neighbour puts the candy on the table and says,"I need to get the phone,so help yourself to whatever kind of candy you want,but please take only one piece." Which of the following would most encourage Harriett to take only one piece of candy?

A) if her neighbour was not able to identify Harriett behind her costume
B) if Harriett is dressed up as a Girl Scout
C) if the candy is placed in front of a Jack-o-lantern
D) if Harriett is two years old rather than twelve years old