Why Does the Fed Have Imperfect Control Over the Money

Why does the Fed have imperfect control over the money supply over short periods?

A) Because of unpredictable changes in reserve requirements
B) Because the public responds to open market operations in unpredictable fashions
C) Because the Fed does not know how much reserves will change when it buys or sells securities
D) Because of unpredictable changes in public desire to hold cash and banks' desires to hold reserves
E) Because of secrecy of FOMC meetings, which lead to policy surprises