Save the day:
反败为胜;挽救局面
例句：
The team was expected to lose, but Sally made three points and saved the day.
本来打算会输的，但Sally进了个三分球，最后反败为胜。
2013NBA总决赛雷阿伦的关键三分球
Late in the day:
为时已晚;坐失良机
例句：
①What with one thing and another, it was fairly late in the day when we returned to town.
忙完这个又忙那个，等到我们回到镇里的时候，天色已经很晚了。
②It's a little late in the day to start talking about policy changes.
现在开始谈论改变政策，已有点为时过晚。
A black day:
倒霉的一天;黑暗的一天
例句：
When we heard the news that David had died, we knew it was going to be a black day for all of his loyal fans.
当我们听到大卫去世的消息时，我们知道对他所有忠实的粉丝来说这将是黑暗的一天。
Kobe
哎，又被戳到伤疤了。。。
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