Answer:
C)

Explanation:
We are given that





We have to find the additional fact which proves that triangle RST and triangle WXY are congruent.
In triangle RST
(Triangle angles sum property)
Substitute the values then we get







When two triangles are congruent then each part of one triangle is congruent to its corresponding parts of another triangle.
Therefore, if

Then,

Therefore,



Hence, option C is correct.