The Exchange Rate Can Be Very Volatile, Yet the Quantity

The exchange rate can be very volatile, yet the quantity of dollars traded might not change much because

A) supply of dollars and the demand for dollars often change in opposite directions.
B) both the demand curve for dollars and the supply curve of dollars are horizontal.
C) the Fed is constantly intervening by buying and selling dollars.
D) supply of dollars and the demand for dollars often change in the same directions.
E) there is only limited quantity of dollars in the foreign exchange market.