Relative clauses perform the following functions EXCEPT that _____.

Relative clauses serve specific functions that enhance the meaning and structure of sentences. They add detail to the main clause, contributing essential or non-essential information that helps clarify who or what is being discussed. When a relative clause is incorporated into a sentence, it often describes a noun, providing a clearer picture of the subject or object.

Furthermore, relative clauses connect to the main clause through relative pronouns like "who," "whose," "that," or "which." This connection is fundamental, as it specifies which person or thing the clause refers to, thereby linking the additional information back to the main idea of the sentence.

The notion that relative clauses might sound more informal than everyday speech does not accurately represent their function. In fact, relative clauses are typically used in both formal and informal contexts, and their structure is essential for clarity and coherence in writing. Therefore, the correct choice highlights the fact that relative clauses do not inherently carry an informal tone; they serve important grammatical roles regardless of formality.