On a unlimited two-dimensional plane, the plane is separated into two-dimensional grid point by line x=k, x=-k, y=k, y=-k (k is integer). There is a game like this : A king could move to any one of the neighbor 8 grid points from the current grid point; The devil could destroy any grid point except the grid point where the king is located; The king couldn't move to the grid point which has already been destroyed by the devil. The initial grid point is (0,0). The king moves firstly, then the devil moves. The question is :
a) what A should satisfy so that the devil has a strategy to win to make the king constraint under line y=A .
b) what B should satisfy so that the devil could constraint the king out of the region x>=B,y>=B.
c) Prove that integer C exists so that the devil has a strategy to win to make the king constraint in the region -C