Final answer:
The best question that maintains a formal tone is option C: What method of refund would you prefer?
Step-by-step explanation:
The best question that maintains a formal tone is option C: What method of refund would you prefer? This question maintains a formal tone by using professional language and shows respect for the customer's opinion. It also offers choices for the customer to decide which method of refund suits them best. By using this question, the writer maintains a professional approach while addressing the customer's concern.
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