GWD13-3-33一个选项是另一个选项的假设,怎么选?

GWD13-3-33:

Wolves generally avoid human settlements.  For this reason, domestic sheep, though essentially easy prey for wolves, are not usually attacked by them.  In Hylantia prior to 1910, farmers nevertheless lost considerable numbers of sheep to wolves each year.  Attributing this to the large number for wolves, in 1910 the government began offering rewards to hunters for killing wolves.  From 1910 to 1915, large numbers of wolves were killed.  Yet wolf attacks on sheep increased significantly.

Which of the following, if true, most helps to explain the increase in wolf attacks on sheep?

1. Populations of deer and other wild animals that wolves typically prey on increased significantly in numbers from 1910 to 1915.
2. Prior to 1910, there were no legal restrictions in Hylantia on the hunting of wolves.
3. After 1910 hunters shot and wounded a substantial number of wolves, thereby greatly diminishing these wolves’ ability to prey on wild animals.
4. Domestic sheep are significantly less able than most wild animals to defend themselves against wolf attacks.
5. The systematic hunting of wolves encouraged by the program drove many wolves in Hylantia to migrate to remote mountain areas uninhabited by humans.

Choice D is exactly the basis of choice C. If domestic sheep are not “ less able than most wild animals to defend themselves against wolf attacks” will the wolves whose abilities of preying on wild animals diminished only attack domestic sheep?

Further more, C has another flaw of NO A, NO B. Are there only two kinds of animals? do they just feed on two kinds of animals without any alternatives? Does their lost-ability of preying on wild animals mean they must attack domestic sheep? All the answers are in question. So I don’t have any clue why C should be the answer.

嗯。这个题我开始做的时候也头疼过。思考了很久才领悟到C，D细微的差别。

sheep, though essentially easy prey for wolves, are not usually attacked by them.这个是解题的一个约束条件。总的说来D和推理没有联系，原因如下：羊群较弱是客观存在的，不是因为狼群捕食能力遭到猎人的削弱才使得羊群较其他动物更易被捕食，D在这点上错误较隐晦，表面读来D项是正确的，可正确还不够，还得满足整个推理的需要。再看C：猎人大量射杀狼，因此极大地削弱了狼群的捕猎能力。这个选项中的因果关系很直白地告诉我们，是猎人促成了这一后果，因此建立了限制条件和结论的关系；再读前面那个约束条件，羊通常情况是不会被狼攻击的。如果按D那么说，狼何不一开始就避重就轻直接去吃羊呢？就是因为这个限制存在。