Which one of the following is an error of principle? (A) A gas bill credited to the gas account and debited to the bank account. (B) The purchase of a non-current asset credited to the asset at cost account and debited to the payables account. (C) The purchase of a non-current asset debited to the purchases account and credited to the payables account. (D) The payment of wages debited and credited to the correct accounts, but using the wrong amount.