Milton Friedman and Edmund Phelps Contributed Which Insight(s)to Phillips Curve

Multiple Choice

Milton Friedman and Edmund Phelps contributed which insight(s) to Phillips curve analysis?

A) that inflation is directly related to expectations of future inflation
B) that inflation is negatively related to the unemployment gap
C) that in the long run unemployment will be at the natural rate
D) all of the above
E) none of the above