In advanced English morphosyntax and word-class categorization, words frequently exhibit categorical dualism, sub-classification anomalies, or functional shifts depending on their syntactic environment. Consider the following four advanced propositions regarding nouns, pronouns, adjectives, and adverbs: I. A deadjectival nominalization preceded by the definite article (e.g., 'the destitute', 'the elderly') functions syntactically as a plural noun head within a noun phrase, requiring plural verb agreement, yet it retains certain adjectival properties such as the capacity to be modified by degree adverbs (e.g., 'the exceedingly destitute'). II. Possessive determiners such as 'my', 'your', and 'their' are historically derived from personal pronouns and continue to be classified in modern generative grammar strictly as pronoun heads occupying argument positions, rather than as functional determiners heading a determiner phrase (DP). III. Flat adverbs—adverbs that share the exact morphological form of their corresponding adjectives without the standard '-ly' suffix (e.g., 'drive fast', 'work hard')—are entirely legitimate elements of standard modern English syntax, functioning as manner adverbs despite lacking typical derivational morphology. IV. Attributive nouns (nouns functioning as modifiers immediately preceding another noun head, such as 'university campus' or 'security protocol') undergo a complete categorical conversion into adjectives, losing all nominal characteristics and acquiring standard comparative and superlative inflectional suffixes (-er, -est). Identify the option that correctly evaluates the grammatical, syntactic, and categorical validity of propositions I, II, III, and IV according to standard English Parts of Speech theory.