In the diagram, \triangle P Q S is equilateral. Also, \triangle P Q R and \triangle P S R are isosceles with P Q=P R=P S. If \angle R P Q=\angle R P S, the measure of \angle Q R S is
Answer Choices
A. 30^{\circ}
B. 60^{\circ}
C. 50^{\circ}
D. 20^{\circ}
E. 45^{\circ}