Which one of the following is the correct concept of Natural rating unemployment ?

The natural rate of unemployment, associated with Milton Friedman and Edmund Phelps, is the unemployment that remains when the labour market is in equilibrium; it consists of frictional unemployment (people moving between jobs) and structural unemployment (mismatch of skills or location). Cyclical unemployment arises from a shortfall of aggregate demand in recessions and is excluded. Any combination that includes cyclical unemployment is therefore wrong.