Since July 2, 2005, China began to implement a managed floating exchange rate system based on market supply and demand, with reference to a basket of currencies, so item C is correct; The typical practice of the dual exchange rate system is to allow all or part of foreign exchange transactions in a country's current account to be conducted in the official market at a fixed commercial exchange rate, while foreign exchange transactions in the capital account and another part of the current account are conducted in the free market at a floating financial exchange rate. Many countries in the world have adopted the dual exchange rate system when developing their own exchange rate systems, including developed countries such as France, Italy and Belgium, and developing countries such as Mexico and Argentina, but China has not adopted it, so AB is wrong. Before 1994, China implemented an exchange rate system in which the official exchange rate and the swap market exchange rate coexisted. However, the exchange reform after 1994 adopts "a single managed floating exchange rate based on market supply and demand", so item D is wrong. So the answer is C.