Which of the following statements is (are) correct? (x) Business cycles are fluctuations in real GDP and related economic variables such as investment and unemployment that occur over time. (y ) A short period of falling incomes and rising unemployment is called a recession and a short period of rising incomes and falling unemployment is called an expansion. (z) During recessions firms may find that they are unable to sell all they produce and, as a consequence, workers are laid off. O a. (x) only O b. (y ) and (z) only O c. (x) and (y ) only O d. (x), (y ) and (z) O e. (x) and (z) only