假设题一道，求牛牛

594davidvilla

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.
题目没看懂，根据有关无关做错了。
答案是A，牛牛给解释一下什么意思。
  还有C怎么不对，文中有elsewhere正好贺outside对应，而且也提到了rice和yam

韩啸0508

A 是说，西非人在种rice和yarms之前，没有别的主要粮食作物
C 说 rice和yarms是西非以外地区最早的农业主要粮食作物。无关

yubem

一篇下来可以排掉BDE，剩下A和C。
A说明在引入R和Y时不会开会什么。所以和原文相关。
C强调什么种植在最早的农业社会，所以和原文无关。

594davidvilla

A 是说，西非人在种rice和yarms之前，没有别的主要粮食作物
C 说 rice和yarms是西非以外地区最早的农业主要粮食作物。无关

-- by 会员 韩啸0508 (2012/3/31 23:24:16)

A是说，一旦rice和yarms被引进，就不再培育主食，是这个意思么。这个assumption对原文有什么作用呢？

韩啸0508

不是这个意思，题目想说的是，不管是在R Y 之前还是之后， 西非人都没有别的主食。。
原文含义是 有了主食才能有 农业， 而 RY是西非"旷古绝今"的主食, 知道了他两什么时候出现，就知道西非农业什么时候开始