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 premier of the new movie.After arriving at the theater,she realizes she left the ticket at home and doesn't have time to return home and get it.Sandy can buy another ticket for $20.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 it is a commitment device to never forget a ticket at home again.