water under the bridge

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释义
过去的就过去了
mean that it happened a long time ago and so you do not feel upset or worried about it now.

例句
Tom： Water under the bridge. We're starting over. So are you ready to take this on?(House of Cards)
汤姆：都过去了，我们要重新开始，那么你准备好了吗?（纸牌屋）