430. I am writing this letter to express my regret for...

谨以此信表达我对于……的遗憾。

本句型是道歉信的开头。其中，regret意为“遗憾；后悔；抱歉”，既可以作名词，也可以作动词。如：

We informed her with regret of our decision. 我们遗憾地把我们的决定告诉了她。句中的介词for后面应该接名词或者名词性短语。此外，regret也可以根据语境替换为apology（歉意），sorrow（悲伤）等词。

Here is my deepest apology for forgetting the appointment we had made. 我把约会给忘了，对此，我深表歉意。

I would like to express my apologies for not being able to keep our 9 o'clock appointment. 对于未能赴9点之约，我深表歉意。

I am sorry that I must apologize for not being able to help you when you asked me to give you a letter of introduction to the director of the National Institute of Oncology of my country. 您要我给我国的全国肿瘤学会负责人写封介绍信一事，我未能帮上忙，对此我深感抱歉。