as a matter of fact

[joham]

--Do you mind my opening the window? It’s a bit hot in here.
--________.

A. Go ahead, as a matter of fact
B. Yes, my pleasure
C. Yes, I do, as a matter of fact
D. Come on

The given answer is C. Some of us think A is fine too. Will native people use A in a situation like this? Thank you in advance.

[tigerpaws]

No, we would not say A because it doesn't make sense. C is correct because the phrase "as a matter of fact" is used to make more forceful the statement "yes I do". If I "mind" it means I do not want you to do it.