GWD-9-20,请求解释

GWD 9-20
Which of the following most logically completes the reasoning?
Either food scarcity or excessive hunting can threaten a population of animals. If the
group faces food scarcity, individuals in the group will reach reproductive maturity later
than otherwise. If the group faces excessive hunting, individuals that reach reproductivematurity earlier will come to predominate. Therefore, it should be possible to determine
whether prehistoric mastodons became extinct because of food scarcity or human hunting,
since there are fossilized mastodon remains from both before and after mastodon
populations declined, and ______.
A. there are more fossilized mastodon remains from the period before mastodon
populations began to decline than from after that period
B. the average age at which mastodons from a given period reached reproductive
maturity can be established from their fossilized remains
C. it can be accurately estimated from fossilized remains when mastodons became
extinct
D. it is not known when humans first began hunting mastodons
E. climate changes may have gradually reduced the food available to mastodons

答案是E ，可是，我还是没有彻底搞懂，请大家再帮忙理理，为什么动物的遗迹都在数量下降的前后能说明是由于食物缺乏造成的呢？还有，如果是由于hunting造成的，那遗迹应该是怎么样的？ 谢谢先啦

答案为B

原文知两个关系：如果FACE FOOD SCARCITY，则慢到reproductive maturity 。如果FACE EXCESSIVE HUNTING，则早到reproductive maturity （早到reproductive maturity 的占大多数）。

所以作者认为有可能确定M是由于FOOD SCARCITY灭绝，还是EXCESSIVE HUNTING灭绝。理由是有M数量减少前后的化石。另外，B说可从化石知道到达reproductive maturity 的平均年龄。因为如果减少前的reproductive maturity 年龄大于减少后的年龄，则原因是EXCCESIVE HUNTING（根据第二个关系）。如果小于，则是FOOD SCARCITY（第一个关系）

太谢谢啦，我也选的是B，可是GWD的答案是E。lawyer哥哥，你也是这个月考嘛？祝顺利呀！

GWD给的答案不是官方答案，不必理它，因为不少错误

LAWYER就是强

这种题目还真要仔细点才能读懂

这种题偶作的时候是把选项一个一个补上去，看能不能解释，好麻烦

A：废话；decline以前的话是当然要多一点，没有提供更多的信息

B：如果能分别确认decline前后的成熟年龄，那么就好办了，比较一下大小

C：when不重要，不是focus

D：first无关

E：气候无关

我觉得关键是减少后的化石，如果能判断成熟年龄较晚，就能说明是由于食物不够（ If the
group faces food scarcity, individuals in the group will reach reproductive maturity later
than otherwise）

如果减少后的化石能判断出成熟年龄早，则说明是被捕杀了 （If the group faces excessive hunting, individuals that reach reproductivematurity earlier will come to predominate.）

但我看不出为什么需要对比减少前后的成熟年龄？