Sandy Is a Big Star Wars Fan and Buys a $20

Sandy is a big Star Wars fan and buys a $20 ticket a week in advance to the premiere of the new movie. After arriving at the theater, she realizes she forgot the ticket at home and doesn't have time to go back and get it. Sandy can afford to buy another ticket for $20, but she decides not to because seeing the movie isn't worth $40 to her. This is an example of:

A) rational behavior, because she values the movie less than $40.
B) irrational behavior, because she really values the movie more than $40.
C) irrational behavior, because the initial $20 is a sunk cost.
D) rational behavior, because she is using the experience as a commitment device against forgetting tickets at home in the future.