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D. Exoskeleton
Exoskeleton is probably the most responsible for the great diversification of insects on land. An exoskeleton is the external skeletons that supports and protects an animal's body, in contrast to the internal skeleton (endoskeleton) of, for example, a human. Examples of exoskeleton animals include insects such as grasshoppers and cockroaches, and crustaceans such as crabs and lobsters.