Answer:
The expenses that went into research and development of a new doughnut flavor
Step-by-step explanation:
A sunk cost is a cost that has already been incurred and cannot be recovered. It is money that has already been spent. Sunk costs are bygone and are not to be considered when deciding whether to continue an investment project.
The expenses that went into research and development of a new doughnut flavor is a sunk cost since the cost has been incurred already and cannot be recovered because it is not a relevant cost.