In the open-economy macroeconomic model, if for some reason foreign citizens want to purchase more U.S. goods and services at each exchange rate, then

a. the demand for dollars in the market for foreign-currency exchange shifts right.
b. the demand for dollars in the market for foreign-currency exchange shifts left.
c. the supply of dollars in the market for foreign-currency exchange shifts right.
d. the supply of dollars in the market for foreign-currency exchange shifts left.

a