Which relationship is always true for the angles r, x, y, and z of triangle ABC? (4 points) A triangle is shown with a leg extending past the top vertex. The vertices are labeled ABC. Angle y is located inside the triangle at vertex B. Angle z is located inside the triangle at vertex C. Angle x is located outside the triangle between beside vertex A and the extended leg. Angle r is located inside the triangle at vertex A. a x + z = y b 180 degrees − x = r c x + y + z = 180 degrees d x + y + z = 90 degrees HEL