Biological change over time accounts for the diversity of species. This diversity a develops through gradual processes over many generations. b occurs in the animal kingdom but not in the plant kingdom. c occurs in the plant kingdom but not in the animal kingdom. d develops only through sudden change over a single generation.

The answer is A. The diversity of species can occur in both plant kingdom and animal kingdom. And for the biological change, the sudden change over a single generation is called mutation. Only when the mutation is good for environment and the environment has changed, the mutation will be reserved and pass to the generations. Then gradually it will accounts the diversity of species.