22. In trapezium $P Q R S$, the sides $P Q$ and $S R$ are parallel. Angle $R S P$ is $120^{\circ}$ and $P S=S R=\frac{1}{3} P Q$. What is the size of angle $P Q R$ ?
A $15^{\circ}$
B $22.5^{\circ}$
C $25^{\circ}$
D $30^{\circ}$
E $45^{\circ}$