A Fixed Exchange Rate System in Which Most Central Banks

A fixed exchange rate system in which most central banks in the world agree to buy or sell dollars as needed to maintain the foreign price of their currency

A) has never existed in the real world.
B) existed before World War I.
C) existed between World Wars I and II.
D) existed between World War II and the early 1970s.
E) has existed since the early 1970s.