What is happening to the U.S. real exchange rate in each of the following situations? Explain. a. The U.S. nominal exchange rate is unchanged, but prices rise faster in the United States than abroad. b. The U.S. nominal exchange rate is unchanged, but prices rise faster abroad than in the United States. c. The U.S. nominal exchange rate declines, and prices are unchanged in the United States and abroad. d. The U.S. nominal exchange rate declines, and prices rise faster abroad than in the United States