Nobody knows for sure how dinosaurs died out 65,000,000 years ago. It _______ because of sudden changes of their living conditions.

A．must have happened

B．would have happened

C．should have happened

D．might have happened

The ABC Bank Irrevocable documentary credit Number: LC123-258866 Date: August 24,1999 Date and place of expiry : October 30, 1999 China Advising bank: Bank of China Beneficiary: China XYZ import and export corp. Applicant: UVW corporation. Amount: USD52,500 (Say U.S Dollars fifty two thousand five hundred only) We hereby issue irrevocable documentary credit which is available with: Any bank By negotiation of beneficiary’s drafts at sight For full invoice value Drawn on the ABC bank Partial shipments: Not allowed Transshipment: Not allowed Shipment from: Shanghai To: Tokyo Japan At the latest: October 15, 1999 Following documents required: +Signed commercial invoice in three copies +Full set of clean on board ocean bill of lading +Weight certificate in two copies Covering: 100 metric tons (5PCT MOL) of XY chemical in drums at USD 500 per M/T. Special instructions: Insurance to be effected by buyer. Instructions to advising bank: Please advise this credit to the beneficiary We hereby undertake that drawers, endorsers in compliance with the terms of this credit will be duly honored upon presentation to the drawee bank. Authorized signature 一、根据上述信用证，回答下列问题

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