Given a text T, and several options, according to the question posed in the text T to choose the most appropriate option from the options as the answer, please directly output the most appropriate option, do not need to output the explanation.

The least likely explanation for why fiscal policy cannot stabilize aggregate demand completely is that:
Option A:private sector behavior changes over time.
Option B:policy changes are implemented very quickly.
Option C:fiscal policy focuses more on inflation than on unemployment.

Answer: B