请解释一下B选项，谢谢

问题如下：

Which of the following is not a reason for why fiscal policy cannot stabilize aggregate demand completely?

选项：

A.

Fiscal policy is subject to recognition, action and impact lags.

B.

The behaviors of private sector are stable.

C.

The policymaker does not have complete information on how the economy functions.

解释：

B is correct.

Private sector behaviour may change over time.

考点：Limitation of Fiscal Policy

解析：因为财政政策存在认识、制定以影响三方面时滞，所以不能够有效稳定住总需求。所以A选项不入选。

私人部门是不断变化的，这才是财政政策不能稳定住总需求的原因，所以B选项入选。

政策的制定者不能掌握所有的关于经济运行的信息，就是产生政策失误，这也是财政政策不能稳定总需求的原因，所以C选项不入选。