Different countries have reached an agreement.
Different countries have came to an agreement.
两种说法都可以标准答案是Agreements have been made between different countries.我想问为什么用between 而不是among涉及事物之间的区别或各国之间的关系时不用among而用between这是特例。另外在 A, B and C在 A、B、C 之间 这种情况时，也用between