Who is not Ash's father in the Pokémon series?

C.) Both A and B.

B.
No one can say for sure if Giovanni isn't Ash's father, and it would actually kind of make sense if he was.
It'd sort of be like the Darth Vader 'I am your father,' thing, huh?
;)

Well, that very confusing:

First of all, in the anime, Delia Ketchum often visits Prof. Oak in his lab, which could be a sign of relationship. For Giovanni, well...if you researched about Pokemon Live! you will find out about Giovanni and Delia having a relationship before Ash was born. Either Prof. Oak or Giovanni Ash's dad, but I believe that Prof. Oak is not his dad cause, well obviously he's old.

c

B

Giovanni is possibly ash's biological father

C