GWD-9-Q40

GWD-9-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?

1. People in western Africa did not develop staple crops that they stopped cultivating once rice and yams were introduced.

2. There are no plants native to western Africa that, if domesticated, could serve as staple food crops.

3. Rice and yams were grown as staple crops by the earliest agricultural societies outside of western Africa.

4. Kola and okra are better suited to growing conditions in western Africa than domesticated rice and yams are.

5. Kola and okra were domesticated in western Africa before rice and yams were introduced there.

我选的Ｂ，答案是Ａ，Ａ也可以理解，可是Ｂ为什么不对？请教，谢谢！

同问！

revise the format of wslinfeng's post for better view

Agricultural societies cannot exist without staple crops没有staple就没有农业社会，但不是有了staple就有农业社会，所以这是necessary condition ，not sufficient。选项a其实不好翻译，太绕，“西非人在大米和yams引入后就就再没有发展（其他的，我的理解）staple crops”本想取非后是：在大米和yams引入手，西非人还发展了其他的staple，也就是说也可能农业社会有可能是在其他的staple引入后建立起来的，这里千万注意文中第一句话：Agricultural societies cannot exist without staple crops表示的是必要条件，不是充分条件，不然的话，文章结论不需要假设了，因为大米和yams最先引入，所以农业社会就是那个年代建立起来的。
B答案显然是在重复文中“All the recorded staple crops grown in western Africa were introduced from elsewhere”，没有任何意义。

A. People in western Africa did not develop staple crops that they stopped cultivating once rice and yams were introduced.

A项翻译为“当rice和yam引进后，西非人就没有发展之前种植的staple crops”。直译为 “西非人没有发展这些，当rice and yam被引入后，就停止种植的staple crops。”

A取反，如果还继续发展了之前的staple crops，那什么时候引进rice and yams就无法和最早的农业社会建立联系。

我试着再解释一下：农业社会的存在不能离开主食（判断的依据），西非所有记录在案的主食都是外来的（现时情况）。因此，想判断西非什么时候开始农业社会，只需要找出主食是什么时候引进过来的就可以了。

现时的情况存在的缺陷：只是所有记录在案的主食，因此只要把这个限制以外的情况都排除掉，结论就能得到加强

A取非后直接对原文产生削弱,说明在R和Y之前,西非就有其他主要作物----正确

B跟原文前提相反,原文已经说了所有的主要作物都是进口来的,做逻辑的时候,要默认原文给的推理前提全部都是正确的,不能推翻原文的推理前提

C说到西非以外的其他农业社会,无关

D是否适合生长跟主要作物的引进无关,即使再适合,它也是补充作物

E中K和O进口得再早也跟主要作物什么时候引进无关