In the Long Run, Unemployment Will Be at the Natural

In the long run, unemployment will be at the natural rate.This implies that

A) there is a one-to-one relationship between unemployment and inflation and consequently, the Phillips curve is vertical.
B) there is no relationship between unemployment and inflation and consequently, the Phillips curve is vertical.
C) there is a positive relationship between unemployment and inflation and consequently, the Phillips curve is upward-sloping.
D) there is a negative relationship between unemployment and inflation and consequently, the Phillips curve is downward-sloping.