The basic enforcement for a foulthis foul in Team A's end zone before a COP is indeed a safety. Team B could indeed elect to have this penalty enforced the normal way and take two points.
However, the test question's answer a. says "Safety. No option." And that is false for two reasons. First, the result of the play is not a safety so team B could decline it and get the ball.
Second, they don't even have to decline it to get the ball: This is a foul by A during a kick that crosses the NZ. (The kick only crosses the NZ thanks to A's bat, but it's still a kick.) So team B can tack on the yardage from the spot where the dead ball belongs to B.
Therefore, they can have half the distance from the B-6, first and goal for them. That makes c. the right answer. (But if c. had said "no option" then it would also be false.)