Final answer:
The sales associate should apologize, admit the mistake, and assure the customer that the situation will be quickly resolved.
Step-by-step explanation:
The sales associate should respond by choosing option d. The sales associate should apologize, admit the mistake, and assure the customer that the situation will be quickly resolved. By doing this, the sales associate can address the customer's concern, take responsibility for the error, and offer a solution to rectify the problem. This approach helps to maintain good customer service and build trust with the customer.