Ann has a credit balance of 18 in Mina plc's receivables ledger. Which of the following would, alone, explain this balance?

A Mina plc issued a credit note for 18 to Ann but miscoded it and it was posted to the account of Ann

B Ann paid an invoice for 18 even though Mina plc had issued a credit note in respect of it

C. Ann paid an amount of 102 in respect of an invoice for 120

D. Ann bought and paid for some goods for 18 which he then returned, but Mina plc has not yet issued a credit note