If the money multiplier decreased from 20 to 12.5, then

a. the Fed increased the reserve ratio from 5 percent to 8 percent.

b. the Fed increased the fed funds rate from 5 percent to 8 percent.

c. the Fed decreased the reserve ratio from 8 percent to 5 percent.

d. the Fed decreased the fed funds rate from 8 percent to 5 percent.