Which of the Following Statements Is True About the Various

Which of the following statements is true about the various exchange rate systems?

A) In a fixed exchange rate system,the value of a currency is adjusted according to the day to day market forces.
B) In a clean float,the central bank of a country will intervene in the foreign exchange market to try to maintain the value of its currency.
C) After the collapse of the Bretton Woods system of floating exchange rates in 1973,the world has operated with a fixed exchange rate system.
D) Under the Bretton Woods system,currency devaluations over 10 percent were allowed only with the approval of the IMF.
E) In dirty float,the exchange rate between a currency and other currencies is relatively fixed against a reference currency exchange rate.