When reconciling its accounts, Ajax Company found the accounts receivable general ledger account had a balance of $30,000, and the accounts receivable subsidiary ledger account balances totaled $28,000. The most likely reason for this difference was:
a) a sale to a customer was recorded twice in the subsidiary ledger
b) cash received from a customer was posted twice to the subsidiary ledger
c) a sale to a customer was not posted to the general ledger
d) cash received from a customer was recorded twice in the general ledger