Agricultural societies cannot exist without staple crops...................fact

Several food plants are known to have been domesticated in western Africa,butthey are all supplemental, not staple, foods.

All therecorded staple cropsgrown in western Africa were introduced from elsewhere, beginning, at some unknown date, with rice and yams............so they are the primary ones

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.............that portion is a bit confusing but note that this choice explains that there are no native staple crops in western Africa prior to rice and yams introduction.

B. There are no plants native to western Africa that, if domesticated, could serve as staple food crops..........One more strong contender. ...................I got stuck between options A and B. Opted for B but found amazing reasons from prashant's and Ron's explanations below.

(B) On negation this statement becomes:
There are SOME plants native to western Africa that, if domesticated, could serve as staple food crops.

Even if there were/are some plants that are staple crops and are native to Western Africa, we don’t know whether these staple crops were planted before the plantation of rice/yams by the agricultural societies, or after staple crops rice/yams were introduced in Western Africa. If it was the former case then it would weaken the conclusion and hence can be a valid assumption. If it is the latter case, then it’s not going to affect the conclusion anyway. Since we don’t know of this information, so this can’t be an assumption - since an assumption is something that must be true for the conclusion to be valid.

Ron: you can also kill B using the negation test.

if you negate B, you get:
There are plants native to western Africa that, if domesticated, could serve as staple food crops.

...to which the answer is:
"ok, great!
but (according to the passage) no one has actually domesticated any of them, so i don't care." the argument is not affected at all. (remember that, when an actual assumption is negated, the argument should be completely destroyed/invalidated.)


C. Rice and yams were grown as staple crops by the earliest agricultural societies outside of western Africa..........we are only aware that they were introduced in western Africa from somewhere else. It does not have to be true that they were staple crops of that region.

D. Kola and okra are better suited to growing conditions in western Africa than domesticated rice and yams are........We dont have to assume this since it is ok even if they are a bit less suited in comparison.

E. Kola and okra were domesticated in western Africa before rice and yams were introduced there.............Does not matter since they are supplemental groups and not staple crops.