In advanced English syntax and subject-verb concord, navigating complex structural anomalies requires precise application of proximity agreement, inverse copular structures, partitive constructions, and coordinated nominal complexes. Consider the following four advanced propositions regarding subject-verb agreement: I. In an inverse copular sentence where the subjective complement and the referential subject differ in grammatical number (e.g., 'The main source of revenue for the enterprise was the fluctuating technology stocks'), prescriptive syntax dictates that the finite verb must agree with the pre-copular predicative complement acting as the logical subject rather than the post-copular noun phrase. II. When a partitive structure consists of a fraction or percentage followed by an of-phrase containing a plural head noun (e.g., 'Two-thirds of the registered voters have cast their ballots'), the finite verb agrees in number with the plural object of the prepositional phrase rather than the singular fractional quantifier. III. When a compound subject consists of coordinated nominals joined by correlative conjunctions such as 'either... or' or 'neither... nor' where the pronouns represent mixed grammatical persons (e.g., 'Neither you nor I are responsible for the financial discrepancy'), standard formal prescriptive grammar dictates that the verb must default to the first person plural form to resolve person conflict. IV. When an expression of measurement, quantity, or collective arithmetic operation acts as a singular mathematical unit (e.g., 'Five times five is twenty-five' or 'Four hours of intensive studying requires immense focus'), standard English grammar permits or mandates singular verb agreement depending on whether the arithmetic or temporal sum is viewed as a unified conceptual entity. Identify the option that correctly evaluates the grammatical, syntactic, and semantic validity of propositions I, II, III, and IV according to standard English grammar and Agreement (linguistics) principles.