Which of the following is an an example of a sunk cost?
a. Jossie purchases a textbook online but returns it because it is the wrong edition
b. Maria goes to a lunch vending machine to get a quick snack. In her haste, she mistakenly pushes the wrong buttons and gets a wheatgrass sandwich instead of hot pocket she was craving.
c. Kennys new smartphone stops working, but it is still under warranty, so he is able to have it repaired at no cost.
d. Antonio goes to the movies. After the opening credits, he realizes he is in the wrong theater. He informs the manager and is able to get a refund.