GWD-9-Q40,求助！自己绕不出来了

珞珞啃书

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.    eople 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.

答案选A，可我总觉得B也对。。。

quellekind

感觉B没有A清楚，

B取反就是：那里有这种native crop，if cultiviated，可以做staple，这个并不导致结论不成立，因为B只是阐述了可能，并没有实现，那些人没有发现，没有耕种，所以A更加直接，切到要害