The main argument in favor of the existence of a natural rate of unemployment, in the long run, focuses on what argument?

a	Firms need to be at full employment in the long run.
b	Workers will adjust their inflationary expectations in the long run so that unemployment is unrelated to inflation.
c	The government cannot affect inflation in the long run.
d	Workers refuse to be unemployed in the long run.
e	Wages will always adjust to make the long-run unemployment rate zero percent.