Which of the following statements about exchange rates is true?
A. Exchange rates were fixed prior to establishing a floating-rate international currency system, and all countries set a specific parity rate for their currency relative either to the Canadian or to the U.S. dollar.
B. Day-to-day fluctuations in exchange rates currently are caused by changes in parity rates.
C. A floating-rate international currency system has been operating since 1973.
D. All of the choices.