A Supplier Sends You a Statement Showing a Balance Outstanding

A supplier sends you a statement showing a balance outstanding of £28,000. Your own records show a balance outstanding of £28,700.
The reason for the difference could be that:

A) You have returned goods worth £700 which the supplier has not yet accounted for
B) The supplier sent an invoice for £700 which you have not yet received
C) You have paid the supplier £700 which he has not yet accounted for
D) The supplier has allowed you a £700 cash discount which you had omitted to enter in your ledgers