GWD9-20是关于化石的鉴别问题，感觉很不好想~~谁来说说~

jyw0411lsq

GWD-9-Q20
Which of the following most logically completes the reasoning?

Eitherfoodscarcity or excessive hunting can threaten a population of animals. If the group faces foodscarcity, individuals in the group will reach reproductive maturity later than otherwise. If the group faces excessive hunting, individuals that reach reproductive maturity earlier will come to predominate. Therefore, it should be possible to determine whether prehistoric mastodons became extinct because of foodscarcity 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
感觉CDE还好，就是在AB 上面很费劲~~~~
还想问一下，题目是不是隐含意思是，动物感觉到危险后（food scarcity，或者hunt),  才开始决定确定繁殖，然后接着不管繁殖的怎么样，就灭绝了？？答案是B
 谁来解释下 B为什么对 ，A为什么不对呗？谢谢各位帮助！

sdcar2010

You got it right.

Answer B is the only choice which clarifies that reproductive maturity age can be determined by studying the fossilized remains.

Answer A does not help to nail down the reproductive maturity age factor.

boozy

如果食物缺乏，M发育慢，就会推迟繁殖的年龄；如果人猎杀它们，繁殖期来得早的种群就容易存活下来。因为有M在种群减少之前和之后的化石，以及（、、、、、）我们就可以推断它们到底死于食物缺乏还是人类捕杀。

A选项：在M种群数量下降前的化石比下降后的化石多。这有什么用啊？只要够分析用，数量少也不怕；如果不够分析，数量再多也没意义。
B选项：从化石中可以分析出M在某个阶段（数量下降前或后）繁殖能力成熟的平均年龄。正解。种群变少年龄变大，是食物；反之是人干的。

jyw0411lsq

恩恩，谢谢LS帮助哈！