Option A: This would directly relate to the president's plan as if the boycott has no effect, there is no reason for management to agree to the union's demand.
Option B: This is also relevant to the discussion. The boycott can not last long if the food products are unavailable at any other store. This means that the union would eventually cave in and buy the products without the management agreeing to their demands.
Option C: This is very less likely to affect the consideration, so we can keep it for now and look at the other options.
Option D: This is also useful question/information. If no other union has been successful in doing such boycotts, it is not very likely that this plan would work out. Also, if such plans have worked out in the past, that must mean that this plan, too, can work out.
Option E: Mega food being the only corporation owing both the grain--processing and food stores is completely irrelevant. The aim is to harm the company profits, even if there are other companies that process with both stores or if there are no other companies in both sectors, it makes no difference in the president's plan.
Comparing options C and E,
C can be relevant in the matter that if there are a large number of stores in the regions, the loss felt by the corporations would be at multiple stores and multiple locations, making the management more likely to agree to the plan.
Further, option E is clearly the least directly relevant question.