The Diagram Below Represents the Exchange Market Position of the United

The diagram below represents the exchange market position of the United States in trade with the United Kingdom.Starting at the equilibrium exchange rate of $3 per pound,suppose the demand for pounds rises from D0 to D1.
Figure 17.1 Foreign Exchange Market

-In the market for British Pounds the demand is represented by D0 and supply by S0.If the exchange rate is allowed to rise as high as $4 and the demand for pounds increases to D1,US monetary authorities will need to

A) supply 8 million pounds to the market
B) supply 4 million pounds to the market
C) supply 2 million pounds to the market
D) do nothing