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题库 / GMATLA-CR-137
Parland's alligator population has been declining in recent years, primarily because of hunting. Alligators prey heavily on a species of freshwater fish that is highly valued as food by Parlanders, who had hoped that the decline in the alligator population would lead to an increase in the numbers of these fish available for human consumption. Yet the population of this fish species has also declined, even though the annual number caught for human consumption has not increased.
Which of the following, if true, most helps to explain the decline in the population of the fish species?
The decline in the alligator population has meant that fishers can work in some parts of lakes and rivers that were formerly too dangerous.
Over the last few years, Parland's commercial fishing enterprises have increased the number of fishing boats they use.
Many Parlanders who hunt alligators do so because of the high market price of alligator skins, not because of the threat alligators pose to the fish population.
During Parland's dry season, holes dug by alligators remain filled with water long enough to provide a safe place for the eggs of this fish species to hatch.
In several neighboring countries through which Parland's rivers also flow, alligators are at risk of extinction as a result of extensive hunting.
情景：Parland地的短吻鳄数量近年因为捕猎而逐年下降。这种短吻鳄以一种淡水鱼为主要食物，这种淡水鱼同样也是当地居民的主要食物。居民们希望短吻鳄数量的下降可以让供人类食用的淡水鱼的数量有所提升，但是却意外地发现，即使人类的捕捞没有增加，鳄鱼的数量也确实下降了，淡水鱼的数量仍然在下降。
推理：本题是一个“现象解释型考题”。按照正常逻辑来说，即，结论应该为：淡水鱼的数量上升了。显然地，本题为因果推理。
顺序的因果逻辑：因为鳄鱼数量下降且人类没有多捕捞淡水鱼，所以淡水鱼的数量上升
（因）前提：鳄鱼数量下降且人类没有多捕捞淡水鱼
（果）结论：淡水鱼的数量上升
选题方式：因果推理只有一个评估方向，简而言之，即，反驳推理文段中的结论。
选项分析：
A选项：鳄鱼数量下降意味着人们可以在以前觉得太危险的地方捕鱼了。由于前提中已经谈到过人类没有更多的捕鱼，所以就算是人类可以在更多的地方捕鱼，也不会影响淡水鱼的数量。
B选项：渔业公司增加了捕鱼船的数量。本选项和(A)的方向几乎相同，同样是不正确的。
C选项：许多Parland的人捕杀短吻鳄是因为鳄鱼皮，而不是因为要保护淡水鱼。本选项讲的是人类以什么原因捕杀鳄鱼，和推理文段的结论无关。
D选项：Correct. 在Parland干燥的季节，由鳄鱼打下的洞穴会储存足够长时间的水来给鱼类提供安全的场所孵化。本选项给出了鳄鱼对鱼群的贡献，可以反驳鳄鱼减少会让鱼类数量上升这一结论。
E选项：在一些Parland的河流流经的地方，短吻鳄由于过度的捕杀而正在面临灭绝的危险。本选项讲的是短吻鳄的情况，和淡水鱼的数量无关。
填坑：It says that the holes dug by alligators can help eggs of this fish. If alligator population has been declining, they won't dug the holes for this fish to hatch. (That is, fishs egg decline, fish decline)
D选项，提供安全场所孵化不是应该是增加鱼类数量吗？