I think what was confusing for me on this question, is that it is not entirely clear to me that there was some kind of "relationship" between the wheat and the barley. That is, as the wheat declined, the barley increased. I took both of these things as being independent of each other. Not sure if this is an assumption embedded in the argument or just an obvious point, but realizing this I can now see why 'B' is the correct answer.

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