Which of the following is a characteristic of vertebrates a) an inner skeleton made of bone or cartilage b) stinging cells c) a hard exoskeleton made of chitin harder outer shell

The answer is A) An inner skeleton made of bone or cartilage. Vertebrates have a column of bones that supports the body and protects the spinal cord, while invertebrates are animals that either have a soft body or a hard outer casing covering their body.

The right option is A) An inner skeleton made of bone or cartilage
Vertebrates are all animals that have vertebra (backbone) with skull and several other skeletal bones which form an endoskeleton. Other characteristic of vertebrates include; they are bilaterally symmetrical with two pairs of appendages, they have higher nervous system, the parts of the central nervous system (the brain and spinal cord) are in the skull and vertebral column respectively and their circulatory system is closed. 

A. radioactive dating