Topic: Interjection,

Best Answer Explained in Below-:

The correct answer is **C: What book do you want?** because in this sentence, "what" functions specifically as an interrogative adjective. Interrogative adjectives are words that modify nouns and are used to ask questions about them.

In this case, "what" modifies the noun "book," indicating that the speaker is seeking specific information about the type or identity of the book in question. The phrase is structured as an inquiry about a noun ("book"), which aligns perfectly with the definition of an interrogative adjective.

In contrast:

- **A** ("What! You don’t mean to say so.") uses "what" as an exclamatory expression, not modifying a noun.
- **B** ("Give me what you can.") employs "what" as a pronoun to refer to an unspecified amount or type of something, rather than as an adjective.
- **D** ("What do you want?") uses "what" as an interrogative pronoun, functioning independently to inquire about the subject's desire.

Thus, C is the only option where "what" correctly acts as an interrogative adjective by directly modifying a noun.