let's pry open the triangles a bit and plug their values for the pythagorean theorem to get the hypotenuse, Check the picture below, those are only the first 4 triangles, notice the hypotenuse.
now let's move like the crab, backwards, let's do D first and then C
D)
well, since for the 1st triangle the root has a "2", that means "1+1", and it's pretty much the same for any subsequent triangle, so the rule must be

C)
what does that make the 9th one?
