Which of the following statements best describes how the passage is organized? A. A description of a phenomenon is provided, and the rest of the passage puts forward hypotheses as to the phenomenon's cause. B. Two phenomena are introduced, and the rest of the passage provides reasons as to why the first is more common than the second. C. A group of species is discussed, and the rest of the passage explains the environmental factors threatening it. D. A phenomenon is described, and the rest of the passage discusses effects of that phenomenon on the environment.