问一道GWD9-40西非农业社会的问题

xiaoyongnao

GWD-9-Q40:

Agricultural societies cannot exist without staple crops.Several food plants, such as kola and okra, are known to have been domesticatedin western Africa, but they are allsupplemental, not staple, foods. All the recorded staple crops grown in westernAfrica

were introduced from elsewhere,beginning, at some unknown date, with rice and yams. Therefore, discoveringwhen rice and yams were introduced into western Africawould establish the earliest date at which agricultural societies could havearisen there.

Which of the following is an assumption on which theargument depends?

A.   People in western Africadid not develop staple crops that they stopped cultivating once rice and yamswere introduced.

B.   There are no plants native to western Africa that, if domesticated, could serve as staple foodcrops.

C.   Rice and yams were grown as staple crops bythe earliest agricultural societies outside of western Africa.

D.   Kola and okra are better suited to growingconditions in western Africa than domesticatedrice and yams are.

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

我选的B，答案是A
B应该错在题目中已经强调了所有的主食，选项中的意思与题中的意思重复
A应该怎么解释呢？好像之前的帖子关于这道题的很少
求各路NN解释！

xiaoyongnao

这道题前辈分析的很透彻，谢谢！

ccmoomer

我的理解：
选项A的含义是：当rice和yams被引进的时候，人们便停止了对主食的培育，并且日后也没再对这些尚未培育成功的主食继续培育。    话中隐含的意思是：在rice和yams主食被引进之前，人们已经开始自己种植培育主食，只是还没等成功，rice和yams便作为主食被引进了，至此，人们便终止了对自己的主食的培育。可以看出，人们自己培育主食的开始时间点，早于rice和yams被引进的时间点。

本题的逻辑链：因为所有生长在西非的主食是从外面引进的rice和yams——所以，追溯rice和yams的引进时间，可以推测出农业社会的诞生时间。

对选项A取not：如果，当它们被最早引进的时候，人们没有停止培育自己的主食，那么，当自己培育主食成功后，rice和yams便不是最早出现在西非社会的主食了。因此，再追溯rice和yams的引进时间便没有了意义，结论不成立。

因此，A选项便是该结论所依赖的假设。