The black envelope is the message containing the loan request.

黑色信封是包含贷款请求的消息。

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Qualification issues include design and testing required to maintain the combat capabilities of the UH-60 Black Hawk and the safe flight envelope of the aircraft with the tank.

该机的设计难点在于用户要求既要保持UH-60原有的攻击运输能力，又要在携带外部大型水箱的情况下保持飞行安全。

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Liberal Democrat AM Peter Black accused Mr Sargeant of drawing up his proposals for legislation "on the back of an envelope".

BBC: Carl Sargeant may force councils to share top jobs