4. Given the hyperbola $\frac{x^{2}}{a^{2}}-\frac{y^{2}}{b^{2}}=1(a>0, b>0)$ with the right focus at $F$, the right directrix at $l$, and a line intersecting the two branches of the hyperbola at points $P$ and $Q$, and intersecting $l$ at $R$. Then ( ).
( A) $\angle P F R>\angle Q F R$
( B) $\angle P F R<\angle Q F R$
( C) $\angle P F R=\angle Q F R$
(D) The size of $\angle P F R$ and $\angle Q F R$ is uncertain