???? ???? ????? ?? ?????????? ?? ??? ??? ??? ??? ??? ?????? ?? ??????? ????? ?? ????? ???? ???? ??? ?? ?? ??? ??? ????? ?? ???? ????? ??? ???? ?? ????? ?????? ?? ????? ??? ??? ???? ???? ???? ???? ?? ??? ??? ????? ?? ???: Option B is suitable simply because "for" is the correct preposition to use with a period of time, for instance "3 a long time".