While I understand why B is the correct answer, I still think that A is more accurate. In the first sentence the author says, specifically, "farmers who grow genetically engineered plants at a LARGE SCALE. are at great financial risk," the "such crops" in the second sentence is clearly in reference to this. The fact that there needs to be qualifier of scale implies that farmers who grow genetically engineered plants smaller scale assume much lower risk. The final sentence implies that they would fetch a high enough price if there was less of a risk. At no point in the passage doesn't the author say that there is not currently demand for these crops, therefore it must be "prudent" to grow these crops on a smaller scale at least for the immediate future.