first order theory

例句：

1. 1. The first order theory of economics is the foundation of modern economics.
   经济学的第一阶理论是现代经济学的基础。
2. 2.This model is a first order theory that explains how to solve complex problems.
   这个模型是一个第一阶理论，解释了如何解决复杂的问题。
3. 3.The first order theory has been proven to be effective in many practical applications.
   第一阶理论已被证明在许多实际应用中是有效的。