1. We can not undo what has been done.
    覆水难收。

2. In general, it's better to undo the problem by adding more iron-rich foods to the diet, because iron supplements can have serious shortcomings.
    一般说来，解决问题的最好方法是在食谱中增加含铁丰富的食物，因为铁离子补剂可能存在严重缺陷。"