The Natural Rate of Unemployment I) Is the Economy's Desirable

The natural rate of unemployment i) is the economy's desirable level of unemployment.
Ii) arises from a single problem that has a single solution.
Iii) is the amount of unemployment that does not go away on its own.

A) i) and ii) only
B) iii) only
C) i) , ii) , and iii)
D) None of the above is correct.