题目内容：
根据下列选项，回答题。Documentary credits are separate transactions from the sales contract with which they are related and Letters of Credit can be divided into many kinds depending on the circum-stances．A documentary credit may be available by payment，by negotiation or by acceptance． 1 means that the nominated bank will pay the beneficiary the full amount due once he submits the correct documents required under the credit．Under a 2 ，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 be transferred by the original beneficiary to one or more parties，it is a 3 ．If a credit is stipulated that its amount can be renewed without specific amendment to the credit being made，it is then a 4． 5 are those that cannot be amended or revoked without the consent of all the parties concerned．
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