When We Say That Economic Fluctuations Are "Irregular and Unpredictable

When we say that economic fluctuations are "irregular and unpredictable," we mean that

A) the relationship between output and unemployment is erratic and difficult to characterize.
B) when one macroeconomic variable that measures income or spending is falling,other macroeconomic variables that measure income or spending are likely to be rising.
C) recessions do not occur at regular intervals.
D) All of the above are correct.