Answer:
a) horizontal at a fixed price level, but vertical at the natural rate of unemployment
Step-by-step explanation:
Phillip Curve was proposed in 1958 by economist A.W. Phillips. The Phillips curve depicts the inverse relationship between inflation and unemployment: as unemployment decreases, inflation increases.
While stable and predictable, in the long run;
Phillips Curve vertical line shows relationship between inflation and unemployment when the economy is at full employment, such that, inflation and unemployment are unrelated in the long run.