Cyclical unemployment refers to a. the relationship between the probability of unemployment and a worker's changing level of experience. b. long-term trends in unemployment. c. year-to-year fluctuations of unemployment around its natural rate. d. how often a worker is likely to be employed during her lifetime.

Option C  

Explanation: The situation when the total demand for goods and services is unable to support the full employment level, then the unemployment arising from such a situations is called cyclical unemployment.

It is a natural phenomenon in every economy as the market forces of demand and supply operate on a very high level and are impossible to control completely.

This type of unemployment always exist in an economy to some extent due to the trends or inflation or deflation.

Thus, from the above we can conclude that the correct option is C.