Harriett Goes Trick-Or-Treating on Halloween

Harriett goes trick-or-treating on Halloween. She arrives at her neighbor's door just as the phone is ringing. Her neighbor 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 Harriet's costume prevented the neighbor from recognizing her.
B) If Harriett was dressed up as a pirate.
C) If the candy was placed in front of a mirror.
D) If Harriett was high in need for cognition.