Final answer:
The relationship between angle 6 and angle 11 is Alternate interior angles.
Step-by-step explanation:
The relationship between angle 6 and angle 11, when lines C and D are parallel, is Alternate interior angles. Alternate interior angles are pairs of angles that are on opposite sides of the transversal and on the inside of the parallel lines. They are congruent, which means they have the same measure. In this case, angle 6 and angle 11 would have the same measure if lines C and D are parallel.