Which of the following statements is true about *causes of business cycle fluctuations?*

A. Economists all agree that supply shocks are the cause of most business cycle fluctuations.

B. Economists all agree that productivity shocks are the cause of most business cycle changes.

C. Economists all agree that monetary changes are primarily responsible for business cycle fluctuations.

D. There are a wide range of theories as to the underlying causes of business cycle movements.