PCAD is hierarchically represented in what?

• A. Grammar rules
• B. Phonemes
• C. Vocabulary
• D. Sentences

Answer: (C)

In PCAD, language knowledge is modeled as a hierarchy where the vocabulary level serves as the central organizing layer. Words carry both meaning and grammatical properties, acting as the bridge between the sounds we hear (phonemes) and the larger structures we produce (sentences). This vocabulary layer supports retrieval of the right word and its syntactic role, which then gets combined according to grammar to form meaningful utterances. Phonemes are the building blocks of sound and are not the overarching representation on which the system is organized. Grammar rules guide sentence structure but are not the repository of word meanings and lexical entries. Sentences are the products built from vocabulary and grammar, not the internal level that structures knowledge within PCAD.