Please answer the following question: Answer the following question given this paragraph: Chordates include vertebrates and invertebrates that have a notochord. Chordates also have a post-anal tail, dorsal hollow nerve cord, and pharyngeal slits. Vertebrate chordates have a backbone, while invertebrate chordates do not. Invertebrate chordates include tunicates and lancelets; both are primitive marine organisms. Q: What do vertebrate chordates possess that invertebrate chordates do not? Choices: - parasite - Thumb - Milk production - backbone A:
A:
backbone