【单选题】The relative purchasing power parity theory postulates that______.
A.
the equilibrium exchange rate is equal to the ratio of the price level in the two nations
B.
the change in the exchange rate over a period of time should be proportional to the relative change in the price level in the two nations over the same time period
C.
change in the exchange rate over a period of time should be proportional to the absolute change in the price level in the two nations over the same time period
D.
the exchange rate at a period of time should be proportional to the relative prices in the two nations