1.表述：flog a dead horse

释义：To continue to focus on something—especially an issue or topic—that is no longer of any use or relevance. （继续做一件毫无成功希望的事情）

例句：We've all moved on from that problem, so there's no use flogging a dead horse.

我们不再讨论那个问题了，再讨论也是白讨论。

The history teacher lectured us every day about the importance of studying history, until we begged him to stop flogging a dead horse.

历史老师每天都给我们讲学习历史的重要性，直到我们乞求他不要白费口舌了。

You're flogging a dead horse by trying to persuade Simon to go to Spain with us.

你劝西蒙跟我们一起去西班牙是在白费功夫。

A: Let’s not talk about it anymore, OK?

我们别谈这件事情了，行吗？

B: Yes, you are right. There is no use flogging a dead horse.

是的，你是正确的，再谈也是白谈。

2.表述：beat a dead horse

释义：To continue to focus on something—especially an issue or topic—that is no longer of any use or relevance. （继续做一件毫无成功希望的事情）

例句：Again and again, I've tried to get senators in my state to ban smoking in restaurants. But it's been hopeless so far; they haven't listened to me. I hate to beat a dead horse but I feel they need to pass this legislation in order to improve public health.

我三番五次想让我们州的参议员设法禁止在餐馆里吸烟，但至今毫无进展，他们根本不理会我。我不想白费劲儿，但是又觉得他们应该通过禁烟的法案，让大众健康受益。

My son's room is a constant mess even though he knows he's expected to keep it tidy. My wife and I have done everything from pleading with him to threatening him, but it's been a waste of our time. We're simply beating a dead horse. He'll never change.

虽然明明知道应该保持整洁，但是我儿子的房间永远是乱糟糟的。我和我太太用尽了各种办法，不管是说服教育还是威逼利诱，都无济于事。他永远都改不了。