In the diagram, \triangle P Q R is right-angled at Q and has \angle Q P R=54^{\circ}. Also, point S lies on P Q such that \angle P R S=\angle Q R S. What is the measure of \angle R S Q ?
Answer Choices
A. 36^{\circ}
B. 54^{\circ}
C. 108^{\circ}
D. 18^{\circ}
E. 72^{\circ}