单选题：根据以下资料回答题Documentary credits are separate transactions from

根据以下资料回答题Documentary credits are separate transactions from the sales contract with which they are relat-ed and Letter of Credit can be divided into many kinds depending on the circumstance. A documen-tary credit may be available by payment, by negotiation or by acceptance. ( 46 ) means that the minated bank will pay the beneficiary the full amount due once he submits the contract documents equired under the credit.Under a ( 47 ), the beneficiary is given double assurance of payment
since the confirming bank has added its own undertaking to that of the opening bank. If a credit can e transferred by the original beneficiary to one or more parties, it is a( 48 ). If a credit stipulated hat its amount can be renewed without specific amendment to the credit being made , it is then a 49 ). ( 50 )are those that cannot be amended or revoked without the consent of all the parties oncerned. A．Confirmed credit
B．Payment credit
C．Negotiation credit
D．Acceptance credit