To weaken the plan, look for what the plan assumes. The fishermen think that selling at a lower price and marketing as a low-fat alternative will increase sales. If customers don't care about price, or don't care about fat intake, the plan has problems.

The only choice to address these weaknesses directly is (E), which tells us that customers aren't concerned about fat intake (their diet). Note that while the other four choices use many key words from the passage, they do not directly engage the fishermen's plan. CR answers are always very closely related to the scope of the passage. (E) is correct.