Concept:A climax community is the stable, final stage of ecological succession.Explanation:In ecological succession, a community keeps changing until it becomes stable.When the climax stage is reached, the types of species and the size of the community stay almost the same for a long time.This stability shows that the community is in balance with its environment.So, a community reaches a climax when its composition and size become constant.Answer:D. the composition and size of a community remains constant over a long period