Which one of the following is an example of a sunk cost?

Multiple Choice

$2,000 in lost sales because an item was out of stock

$2,000 paid last year to rent equipment

$2,000 project that must be forfeited if another project is accepted

$2,000 reduction in Product A revenue if a firm commences selling Product B

$2,000 increase in comic book sales if a store ceases selling puzzles