Let \( A = \left\{ z \in \mathbb{C} : \left| \frac{z + 1}{z - 1} \right| < 1 \right\} \) and \( B = \left\{ z \in \mathbb{C} : \arg \!\left( \frac{z - 1}{z + 1} \right) = \frac{2\pi}{3} \right\} \). Then \( A \cap B \) is:
A portion of a circle centred at \( \left( 0, -\frac{1}{\sqrt{3}} \right) \) that lies in the second and third quadrants only
A portion of a circle centred at \( \left( 0, -\frac{1}{\sqrt{3}} \right) \) that lies in the second quadrant only
An empty set
A portion of a circle of radius \( \frac{2}{\sqrt{3}} \) that lies in the third quadrant only