During the last three decades, the number of people participating in physical fitness programs___ sharply.

A．was increasing

B．has increased

C．had increased

D．will be increasing

因果关系预测方法包括( )。

A．投入产出模型

B．指数平滑法

C．回归分析

D．季节变动预测法

E．经济计量模型