ACT真題每日一練2.2_Hopetrip旅遊網

　　Science Question for Tuesday, February 2nd, 2016

　　Abandoned cornfields have been the sites of investigations concerning ecological succession, the orderly progression of changes in the plant and/or animal life of an area over time (see Figure 1).

　　(Note: The plants are ordered according to their appearance during ecological succession.)

　　During the early stages of succession, the principal community (living unit) that dominates is the pioneer community. Pioneer plants are depicted in Figure 2.

　　The final stage of ecological succession is characterized by the presence of theclimax community, the oak-hickory forest. Figure 3 depicts the gradual change from pine to hardwoods.

　　Figures adapted from Eugene P. Odum, Fundamentals of Ecology. ©1971 by Saunders College Publishing/Holt, Rinehart, and Winston, Inc.
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　　On the basis of the data depicting the gradual change from pine forest to an oak-hickory forest, after 100 years, as the density of the pine trees:

　　A. increases, the density of the oak-hickory trees increases.

　　B. increases, the density of the oak-hickory trees decreases.

　　C. decreases, the density of the oak-hickory trees increases.

　　D. decreases, the density of the oak-hickory trees decreases.

　　謎底：C

　　【剖析】The best answer is C. Figure 3 depicts the gradual change from pine forest to an oak-hickory forest and is therefore the correct figure to use in answering this question.

　　Figure 3 indicates that after 100 years, the density of pine trees steadily decreases from approximately 3,500 trees per unit area at Year 100 to approximately 750 pine trees per unit area by Year 200. Likewise, Figure 3 indicates that after 100 years, the density of oak-hickory trees steadily increases from approximately 4,000 trees per unit area to approximately 22,000 trees per unit area by Year 200. Thus, C is correct.