One Thing the Fed Has Learned Over the Past Twenty-Five

One thing the Fed has learned over the past twenty-five years is:

A) The money multiplier is fairly constant no matter what changes are made to the monetary base
B) The theory of the money multiplier isn't very useful since the money multiplier is unstable over time
C) The money multiplier has a trend rate of growth that is fairly constant
D) It should focus its attention on targeting M2