From step #6, AB is congruent to CD by CPCTC or Corresponding Parts of Congruent Triangles are Congruent.
Triangles ABE and CDE are congruent by SAS postulate.
Therefore, angle B and angle D are congruent.
Note that the segment BD is a transversal line that cuts AB and CD, and angle B and angle D are alternate interior angles.
The answer is :
XY || WZ ⇒ AB || CD
with a reason of :
Parallel lines cut by a transversal form congruent alternate interior angles.