GMAT Critical Reasoning (CR) | Re: Agricultural societies cannot exist without staple crops.

It is always better to simplify the argument -

Premise 1 -Agricultural Societies --> Staple Crops
Premise 2 -Rice and yam --> First Staple Crops in Africa

Conclusion -Time when rice and yam were introduced --> Start of Agricultural Societies in W.Africa

Let us look at each of the answer options -

A - let us negate this answer option.
"people developed staple crops before rice and yam were introduced" - this statement weakens the conclusion. If this were indeed true,
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