Hierarchical classification orders taxonomical categories from most to least inclusive. The correct descending sequence is:
• Phylum (C): A high-level category grouping related classes.
• Class (D): Includes related orders within a phylum.
• Order (B): Contains families sharing common characteristics.
• Genus (A): A group of related species.
Thus, the correct order is (C) → (D) → (B) → (A).