Explanation

The term "syntax" refers specifically to the set of rules and principles that govern the structure of sentences in a language. It encompasses how words and phrases are arranged to create meaningful and grammatically correct sentences. This includes elements such as word order, sentence length, and the relationships between different parts of a sentence.

While options A, B, and C touch on aspects of language and writing, they do not accurately represent the definition of syntax. For instance, option A mentions pronunciation, which falls under the domain of phonetics rather than syntax. Options B and C refer to rules for essays and paragraphs respectively, neither of which focus specifically on sentence structure. Thus, option D, "Rules for sentence building," precisely captures the essence of syntax, as it directly pertains to how sentences are formed and organized.

To help remember the answer, think of the key elements related to syntax: Sentence Structure, Word Order, Grammar Rules, Sentence Formation. These terms highlight the core concept of syntax in a way that reinforces its importance in constructing coherent and effective sentences.