25. 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 reproductive maturity 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
What the argument says is that:
food scarcity --> reaching rereproductive maturity later than normal, therefore the average age to reach reproductive maturity will be older than normal.
excessive hunting --> reachineg reproductive maturity earlier than normal, therefore the average age to reach reproductive maturity will be younger than normal.
Apparently, the average age to reach reproductive maturity BEFORE the extinction was the NORMAL average.作者: zdytiffany 时间: 2012-12-11 06:38
Read this sentence: since there are fossilized mastodon remains from both before and after mastodon populations declined,
So you have two populations: before and after the decline. From the population before the decline, you can obtain the NORMAL age to reach reproductive maturity. Then you can obtain the average age to reach reproductive maturity AFTER the decline. Compare these two number. If the former is bigger than the latter, excessive hunting is the cause. If the former is smaller than the latter, food scarcity is the cause.作者: saintaa 时间: 2012-12-12 21:22
Either food scarcity or excessive hunting can threaten a population of animals. （食物稀缺与捕杀过多都会威胁动物族群）
If the group faces food scarcity, individuals in the group will reach reproductive maturity later than otherwise.（食物稀缺时，生殖年龄会后延）
If the group faces excessive hunting, individuals that reach reproductive maturity earlier will come to predominate. （捕杀过多时，生殖年龄会提前）
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 （因此，要判断史前某种动物灭绝的原因是可能的，因为有物种减少前后的化石而且...）.
(A) there are more fossilized mastodon remains from the period before mastodon populations began to decline than from after that period（物种减少前的化石比减少后的化石多）
(B) the average age at which mastodons from a given period reached reproductive maturity can be established from their fossilized remains（可从化石判定生殖期在何时）
(C) it can be accurately estimated from fossilized remains when mastodons became extinct（可从化石估计灭绝的时间）
(D) it is not known when humans first began hunting mastodons（人类开始狩猎这种动物的时间并不可考）
(E) climate changes may have gradually reduced the food available to mastodons（气候变更使食物变得稀缺）作者: zdytiffany 时间: 2012-12-14 06:38
