M. A. K. Halliday made quite clear his point of view that lingui

M. A. K. Halliday made quite clear his point of view that linguistic events should be accounted for at three primary levels: substance, _____, and context.
【正确答案】：form
【题目解析】：韩礼德认为语言材料可以在三个层次上进行解释，实体、形式和语境。实体指语言原材料，即声音上或书写上的符号；形式指把实体排列成有意义的结构，包括语法和词汇；语境是语言出现的场合。所以，本题填form。