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Option B is incorrect. Segmentation is the repetition of body parts within separated portions of the body. Option C is incorrect. Body symmetry refers to the division of the body along an imaginary axis or axes. Option D is incorrect. Nerve nets are a diffuse network of nerves used to carry information to and from the parts of the body in invertebrates that have no centralized brain. Option A is correct. Cephalization is the centralization of nerves at one area of an animal and are usually contained within a brain.