The U.S. dollar appreciates, and U.S. official reserves increase. Explain which of the following events might have caused these changes to occur and why.

• The Fed intervened in the foreign exchange market and sold U.S. dollars.
• The Fed conducted an open market operation and sold U.S. bonds.
• People began to expect that the U.S. dollar would appreciate.
• The U.S. interest rate differential narrowed.