How Would You Measure the Angular Momentum of a Black

How would you measure the angular momentum of a black hole?

A) Place a satellite in orbit outside the event horizon and measure its period.
B) Place two satellites in orbits in opposite directions and compare their periods.
C) Release an object to fall into the black hole, and then watch to see if its path curves.
D) Set a pole at rest outside the event horizon, pointing toward the black hole. If the pole begins to spin, the black hole has angular momentum. The amount is determined from the spin rate.