Who are you referring to, to whom are you referring, whom are you referring to?
Who are you talking to, to whom are you talking, whom are you talking to?
I am not sure, but I think that only to whom are you referring/talking is correct. 'To who' is impossible. There must be a grammar rule that teaches this I hope.
Thanks
Top answer
Hi, The following are OK: Who are you referring to? (casual) To whom are you referring? (formal) Whom are you referring to?
— Regards
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