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.