参考答案

正确答案：
system-structure[解析] J. R. Firth's main approach to the notion of function in context was by means of concept system. People refer to his theory as system-structure theory.
弗尔斯构想根据语境功能这一概念来建立自己的语言学理论，而达到这一目的的主要途径是借助于系统概念。由于系统在他的理论中占据重要地位，所以他的理论被称为系统结构理论。