Answer: D) Two
You need the starting point, and another point that helps direct where the ray is aimed. Call these two points A and B.
Saying "Ray AB" means we extend a line through AB such that the line goes forever through B and beyond B, but we do not do the same for point A. The point A is effectively a cliff where no road goes on the other side of it. Check out the diagram below to see what I mean. The arrow means the line goes on forever in that direction.