A、The ultimate buyer. B、The middleman. C、The issuing bank. D、The actual supplier. C录音原文提到However，the“back—to-back”credit comes i

Back-to-Back credits consist of two entirely separate documentary credits, but one credit may act as security for the other. They apply in transactions when actual suppliers and ultimate buyers deal through a middleman. If the supplier insists on a documentary credit, the middleman may apply to his bank for a credit on his behalf. If the middleman’ s bank is satisfied with his creditworthiness, the bank will issue the credit in the normal way and no other formalities will apply. However, the "back-to-back" credit comes into use if the bank insists that the middleman obtain a documentary credit in his favor from the ultimate buyer as security for the "back-to-back" credit in favor of the actual supplier. Only the middleman and his banker know the "back-to-back" credit, and only they are concerned with credit.
25. What do the back-to-back credits consist of?
26. In which situation do the back-to-back credits apply?
27. In whose favor is the back-to-back credit issued?