Step 1: Definition of Semi-Synthetic Polymers Semi-synthetic polymers result from the chemical alteration of natural polymers. Illustrative examples are cellulose derivatives and altered rubber. Step 2: Categorization of Provided Choices Cis-polyisoprene represents natural rubber and is thus not a semi-synthetic polymer. Cellulose nitrate and Cellulose acetate are cellulose derivatives that have undergone modification. Vulcanized rubber is natural rubber subjected to chemical treatment, qualifying it as semi-synthetic. Conclusion: As cis-polyisoprene is natural rubber, the accurate selection is (A).