Within the activity of sterilization, "defensive" purchases or sales of government securities by the Federal Reserve are a. open-market operations undertaken during periods in which the United States has been at war. b. open-market operations that are undertaken to prevent other factors from bringing about undesired changes in the monetary base. c. open-market operations directed specifically at effecting net decreases in the monetary base, d. open-market operations directed specifically at effecting net increases in the monetary base. e. open-market operations directed toward initiating monetary policy