Answer:
C. Prove that angle VXW = angle YXZ by vertical angles.
Explanation:
If Reiko wants to use AAS, she needs to find two pairs of congruent angles and one pair of congruent sides.
She already knows the side WV = side YZ, so that's S.
She also knows that angle WVX = angle XYZ, so that's one A.
What's left is one more A for her to find: so we know the answer cannot be A or D, because those are sides, not angles.
The clearest one to prove is choice C, because those are clearly vertical angles.