A small arrow moves one cell forward in the direction it points. When the next cell would be off the board, it stays put and turns a quarter turn clockwise instead. Which board comes next?

The arrow moves right along the top row to the corner. It cannot go further right, so it turns clockwise to face down (fourth board). Now the cell below is free, so it moves down one cell, still facing down: (c). (a) turns again instead of moving, (b) moves but faces right, and (d) moves diagonally.