The Schwarzschild Radius of a Black Hole Is the Distance

The Schwarzschild radius of a black hole is the distance from the singularity (center) to the:

A) point where the gravitational field becomes zero.
B) event horizon, from which light cannot escape.
C) outside radius of the massive solid body forming the black hole.
D) accretion disk, from which x rays originate and from which light can still escape.