A segment through the focus F of a parabola with vertex V is perpendicular to \overline{F V} and intersects the parabola in points A and B. What is \cos (\angle A V B) ?
Answer Choices
A. -\dfrac{3 \sqrt{5}}{7}
B. -\dfrac{2 \sqrt{5}}{5}
C. -\dfrac{4}{5}
D. -\dfrac{3}{5}
E. -\dfrac{1}{2}