Refer to the graph shown. A shift in the supply of dollars from S1 to S2 is most likely the result of:

A. a decrease in the U.S. price level relative to foreign prices.
B. an increase in U.S. incomes relative to foreign incomes.
C. the U.S. government's attempt to support its own currency.
D. an increase in U.S. interest rates relative to foreign interest rates.

Answer: B