Concept:The graph shows a stepped or discontinuous growth curve.Explanation:Insects possess a rigid exoskeleton that cannot expand gradually.Growth occurs in distinct stages separated by moulting, or ecdysis.Each moult is followed by a sudden increase in size, creating a step-like pattern.Between moults, little or no growth is observed.Cestoda, Reptilia, and Amphibia do not show this type of discontinuous growth.Answer:D. Insecta
