In the diagram, PQ is parallel to RS. Also, Z is on PQ and X is on RS. If Y is located between PQ and RS so that \angle{YXS}=20^\circ and \angle{ZYX}=50^\circ, what is the measure of \angle{QZY}?
Answer Choices
A. 30^\circ
B. 20^\circ
C. 40^\circ
D. 50^\circ
E. 60^\circ