why is the long-run philips curve vertical?
a) the long-run philips curve is vertical because the natural rate of unemployment never changes.
b) the long-run philips curve is vertical because any level of inflation can occur at the full-employment rate of unemployment in the long run.
c) the long-run philips curve is vertical because any level of unemployment can occur at the full-employment rate of inflation in the long-run.
d) the long-run philips curve is vertical because it represents a relationship between two real variables in the long run.
e) the long-run philips curve is vertical because the inflation rate is always the same.