大家讨论一下这个题，大家觉得正确答案是哪个呢？

akatsuki09

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 Africathat, if domesticated, could serve as staple food crops.

C.     Rice and yams were grown as staple crops by the earliestagricultural societies outside of western Africa.

D.     Kola and okra are better suited to growing conditions inwestern Africa than domesticated rice and yamsare.

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

moonlolita

正是因为原文严密，所以我觉得，我们可能要搞清原文真正想排除的是原文哪段推理部分的薄弱环节

A和B，我觉得都可以做为答案，但是，B有一点不太好，就是我觉得他不如A对应原文的RECORD的那个词的针对性更明显。就是说，如果B对，那么必须成立的是，从古至今，所有NATIVE的FOOD都不是STAPLE，和有RECORD这个前提关系不密切了；
但A就排除了这个可能，就是说排除了“在有record之前，农业社会就已存在过，只是没被RECORD，而直到外来物种被引进，才有了RECORD”这种可能

akatsuki09

I'm sorry mate.The correct is A. and I'm confused now.

leadwest

在下拙见：
B.      There are no plants native to western Africa that, if domesticated, could serve as staple food crops.
原因：原文是完整的逻辑推理。结论是说：rice and yams 的引入导致了西非农业社会的形成。
B 选项去掉NO以后是对原文的削弱。（其他农作物也可以作为staple food，不一定非得是rice and yams）
原文非常严密，recorded(有记录的) staple crops并没有排除西非存在别的本地domesticated农作物作为staple food的可能性。