I am writing to express my apology to you.

第一个,expree这个词用在书面上多一些,说出来显正式~
再问： i feel so sorry和i fell terrible sorry
再答： I feel terribly sorry才对哦，用副词形式~这个terribly用处非常多，比如the test is terribly difficult. Again, I would like to apologize for any inconvenience this may have caused yo Once again, I feel so sorry for any inconvenience caused. Please accept my apologies. 再次为给您可能造成的不便向您道歉~请接收我的道歉！