Alex changed his mind at the last minute，otherwise we an agreement.A. should have reached

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A. should have reached
(答案→)B. could have reached
C. can reach
D. should reach
解析：
句意为：亚历克斯最终改变了主意，否则的话我们就会达成一致了。对过去事情的推测，应该使用“情态动词＋have done”。should have done应该已经做了……；could have done很可能已经做了……。所以应该选择B项。