(一).(That's) Water under the bridge. 忘记发生过的事吧！

原音重现：
A:Weren't you angry with Bob last year?
去年你没对鲍勃发过火吗？
B:I was, but that's water under the bridge.
发是发过，但那是过去的事了。
英英释义：
This is a way of saying "Let's forget about it." It is said to indicate something happened in the past and should be forgotten.
美剧表达：
1.Oh, it's water under the bridge. Forget it!
都是过去的事了，忘了吧！

(二).I seem to have lost track of it. 我好像已经忘记了。/好像已经记不得了。

原音重现：
A:Can I borrow your English dictionary.
能借你的英语词典用一下吗？
B:I'm not sure where it is. I seem to have lost track of it.
我不知道在哪儿，我忘记放哪儿了。
英英释义：
This indicates something was forgotten or not kept in touch with. It is like saying "I don't remember where it is" or "I didn't stay in touch."
美剧表达：
1.I'm sorry. I guess I lost track of time.
对不起，我忘记时间了。