自然生态系统中，生态位的确定是（）。

A、物种竞争形成的

B、物种演化形成的

C、物种变异形成的

D、自然形成的

Which of the following theories suggests that both aggregate demand and aggregate supply are primarily driven by changes in technology over time（）

A. Neoclassical school.

B. Keynesian school.

C. Austrian school.