GWD-9-40

cranberry

文章的逻辑关系如下：前提是无主要作物就无农业社会，论据是在米和番薯引入西非之前，西非没有主要作物，结论是西非的农业社会是从米和番薯的引入开始的（文章中是时间）。其假设必定要是在米和番薯之前，西非没有主要作物。a说明，此前确实没有。b说的没有作物具有成为izhuyao作物的可能。其实有或者没有都与本题无关，因为即使有，也不影响结论。

umclaire

a is a required condition,b is a sufficient condition, very triky.

shifeng

A

流沙

以下是引用horsefish在2004-9-18 9:00:00的发言：

选A.

B的问题是否定的是没有native, 万一以前在rice和yam引进以前存在其他引进staple crops,那么农业开始的日期也不是从rice和yam开始, 只有A彻底让你相信在rice和yam引进以前不存在其他staple crops.(偶的逻辑都是大白话)

这个解释看着最易懂了。总也学不会取非

Andrea625

A 的说法是排除了原来有主要作物的可能。如果原来有主要作物（不是后来引进的这个）只是在引进这个新作物之后不耕种原来的了（从另一个角度说原来有主要作物），就影响了推理过程。对吧？

[此贴子已经被作者于2004-10-7 14:52:47编辑过]

zhaoshujuanw

看了以上各位的讨论，终于明白了。选A.

howru

我觉得.   A) People in western Africa did not develop staple crops that they stopped cultivating
once rice and yams were introduced.  其实已经和文章中已经有的前提矛盾了 - "Several food plants, such as kola and okra, are known to have been domesticated in western Africa, but they are all supplemental, not staple, foods."   这似乎已经很明白地说 rice 和yams引用之前没有其他作物了嘛.    所以 A) 似乎很有点问题的.   当然B) 也不对.

我觉得答案应该是 C) (怎么没有人选 C 啊?   ).  既然要从最早的 rice 和yam的引入来作为西非农业开始, 那必须有其他地区的农业早于西非, 这就是 C) - Rice and yams were grown as staple crops by the earliest agricultural societies outside of western Africa.

Some may argue that 你这不也和前提矛盾了吗? 因为文章中已经明说 - All the recorded staple crops grown in western Africa were introduced from elsewhere, beginning, at some unknown date, with rice and yams.  我狡辩道: 注意那个"recorded".   recorded 不等于 最早的啊.

BTW, 楼主的题目可能是 key-in 的(if true, 好辛苦啊, 赞叹!) , 好象标点有点不对, for 完整 sake, I copy and paste the question and answers as follows:

Q40:
Agricultural societies cannot exist without staple crops. Several food plants, such as kola and okra, are known to have been domesticated in western Africa, but they are all supplemental, not staple, foods. All the recorded staple crops grown in western Africa were introduced from elsewhere, beginning, at some unknown date, with rice and yams. Therefore, discovering when rice and yams were introduced into western Africa would establish the earliest date at which agricultural societies could have arisen there. Which of the following is an assumption on which the argument depends?

A. People in western Africa did not develop staple crops that they stopped cultivating once rice and yams were introduced.
B. There are no plants native to western Africa that, if domesticated, could serve as staple food crops.
C. Rice and yams were grown as staple crops by the earliest agricultural societies outside of western Africa.
D. Kola and okra are better suited to growing conditions in western Africa than domesticated rice and yams are.
E. Kola and okra were domesticated in western Africa before rice and yams were introduced there.

bobwangwb

to howru

c不对，注意c中的“as staple crops ”，假设西非之外的某地种Rice and yams ，但不是as staple crops ，结论一样成立。故c取非不weaken。

我想你的问题是这句话理解过于集中于outside of western Africa，其实一个选项如果作为假设的正确答案，那么对这个选项的逻辑要求是很高的，不能有任何纰漏，c有上述漏洞，不是正确选项。

另外，我的一个做题经验是，假设的正确答案往往是很focus，只说一个问题，因为这样漏洞小，往往正确。

请指正

scorpio0001

谁能帮我解释一下A选项的具体意思：

A. People in western Africa did not develop staple crops that they stopped cultivating

once rice and yams were introduced.

高亮部分不明白，请哪位高手翻译一下。个人感觉that是引导staple的定语从句。怎么叫stop cultivating。

[此贴子已经被作者于2005-3-10 17:10:27编辑过]

lingbaitao222

银钩铁划 , 你的名字太酷, 是不是对GMAT的仇恨太大,还是想把GMAT的同伴菜了,

我是GMAT四月革命党员,您呢?