The answer is the third statement. "The triangles are congruent because triangle R'S'T' is a rotation of triangle RST and rotation in a rigid motion" The triangles are congruent because the image is a rotation (There is a rotation of 180 degrees) of the original and a rotation is a rigid motion. The best way to test it out is to assign values to the points for points R, S, and T and then apply the rule to see where the new image will be.
