他对她咧嘴一笑，表示遗憾。

He grinned at her ruefully.

《柯林斯英汉双解大词典》

澳大利亚谴责了这次试验，美国对此表示遗憾。

Australia condemned the test and the US expressed its regret.

youdao

我对这样的结局表示遗憾。

I'm sorry it ended like that.

youdao

And I mean, at a certain point, you have to make a decision and I'm sorry for the minority but sometimes, it's for the general, for the greater good.

有时，你必须做出选择,我对少数表示遗憾,但有时，这是牺牲小我，成全大我。

耶鲁公开课 - 公正课程节选

that something you that you either did or did not do but should have done.

为一些你之前做过的或是本该做却没有做的事情表示遗憾。

I should have 课堂 - SpeakingMax英语口语达人