When Economists Say That There Is a Time Lag in the Effect

When economists say that there is a time lag in the effect of monetary policy,what do they mean?

A) That it takes time to observe the effects of fiscal policy on the economy
B) That the Fed takes awhile to figure out what it wants to do
C) That the Congress takes awhile to figure out what it wants to do
D) That it takes time to observe the effects of monetary policy on the economy
E) That the public needs time to decide how to respond to monetary policy changes.