The five sides of a regular pentagon are all equal in length. Also, all interior angles of a regular pentagon have the same measure. In the diagram, P Q R S T is a regular pentagon and \triangle P U T is equilateral. The measure of obtuse \angle Q U S is
Answer Choices
A. 172^{\circ}
B. 168^{\circ}
C. 170^{\circ}
D. 176^{\circ}
E. 174^{\circ}