According to Economics Theory, Challenges to implementing a discretionary fiscal stimulus in a timely manner are least likely to include the:（）

A. government payments for unemployment benefits.

B. need to convince lawmakers that action must be taken.

C. inability of policymakers to forecast a recession precisely.

现代生理学的起点是  

A．细胞学说的确立

B．微生物学说基础的奠定

C．制定出植物分类法

D．血液循环学说的建立