A stakeholder argues that a half-built feature must be finished because the company has already spent nine months on it. Which economic term names this reasoning, and what is the correct treatment?

• AOpportunity cost, and it means the feature should be finished to recover the investment.
• BCost of delay, and it means the feature should be finished quickly.
• CTotal cost of ownership, and it means the feature is now too expensive to abandon.
• DSunk cost, and it is irrelevant to the next decision, since the nine months are gone under every option and cannot be recovered by spending more.