passage 21 海洋生态系统不像陆地生态系统那样好操作
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文章讲解：
①Our terrestrial food supply comes from ecosystems transformed to produce a few comestible species through the removal of competitors, predators, and pests, but marine capture fisheries depend on the overall productivity of natural ecosystems. ②There is, however, increasing concern about the impact of fishing and other human activities on marine ecosystems, which are now far from pristine. ③One option for moving toward both biodiversity and terrestrial food supply goals is to produce greater yields from less land, thereby freeing land for conservation purposes. ④By contrast, the objective of maintaining or restoring the biodiversity of marine ecosystems may conflict with the objective of maintaining or increasing our food supply from the sea, since the level of fishing required to achieve the latter may compromise the former.
①现象，客观对比 T vs M ↔ ② 提出问题 M
↓
③ 给出办法 T ↔ ④ 提出对比 M
1. The primary purpose of the passage is to 主旨
B
A. Examine the impact of certain research findings regarding changes to ecosystem biodiversity. IR，同时没有体现文中对比
B. Discuss a possible implication of a difference between terrestrial and marine food supply sources. 重在对比
C. Describe the consequences of a certain kind of interaction between terrestrial and marine ecosystems. NE
D. Identify an area of ecosystem research in which there are significant uncertainties. NE
E. Present evidence that undermines one side of a debate about biodiversity and supports the other. 三个NE
D干扰，主看论证框架
2. According to the passage, increasing the food yield per unit of land can have which of the following effects? 直接细节，对应③
E
A. Enabling more land to be used for development purposes NE
B. Compromising progress toward conservation goals
C. Helping protect comestible species from competition and predation NE/IR
D. Helping reduce pressure on marine ecosystems IR
E. Helping restore the biodiversity of terrestriale cosystems
A干扰，选项要看完。单选选最优。
