Refer to the diagram where D and S are the United States' demand for and supply of Swiss francs. At the equilibrium exchange rate, E, the United States' balance of payments is in equilibrium. A shift of the demand curve to D' might be the result of:

A.  a relative decline in interest rates in Switzerland.

B.  a reduction in the United States' relative price level.

C.  a recession in the United States that slows its rate of growth.

D.  a relative decline in interest rates in the United States.

D.  a relative decline in interest rates in the United States.