Final answer:
The creativity of language, known as mental grammar, is governed by syntactic rules, reflecting our inborn capacity to produce and understand language.
Step-by-step explanation:
The creativity of language, or mental grammar, is governed by c) Syntactic rules. Mental grammar refers to the innate set of rules and principles that human brains use to produce and understand language. This includes the use of semantics (deriving meaning from words) and syntax (the arrangement of words into sentences). Our remarkable ability to generate limitless new sentences that others can understand relies upon this deep-seated syntactic knowledge, which goes far beyond a mere list of vocabulary words from our lexicon. Children acquire these syntactic rules naturally, showing that language is not solely learned through reinforcement but also through a biological predisposition to grasp and construct language systems.