Which relationship is always true for the angles x, y, and z of triangle ABC? 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 side AC and the extended leg.

x + z = y
y + z = x
x + y + z = 180 degrees
x + y + z = 90 degrees