The correct answer is: B. Credit note
A credit note is a document issued by a seller to a buyer to acknowledge the return of goods or the cancellation of a sale. It is used to reduce the amount owed by the buyer to the seller.
A debit note is a document issued by a buyer to a seller to acknowledge the receipt of goods that are not in accordance with the terms of the sale. It is used to increase the amount owed by the seller to the buyer.
A proforma invoice is a document that is sent to a buyer before goods are shipped. It is used to confirm the terms of the sale, such as the price, quantity, and delivery date.
A bill is a document that is sent to a customer to request payment for goods or services that have been provided.
In the case of a customer returning goods, the seller would issue a credit note to the customer. The credit note would reduce the amount owed by the customer to the seller.