Could you please evaluate each of the four sentences depending on whether it is natural? Besides, in a case like this, should we use "about" instead of "for" in modern English?
(A) I'm very sorry for not introducing myself earlier.
(B) I'm very sorry for not introducing myself until now.
(C) I'm very sorry for not having introduced myself earlier.
(D) I'm very sorry for not having introduced myself until now.
All 4 are fine. 'for' is better, more direct.
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