A does not have to be true. The passage tells us that if we adopt the scientists proposal, then some farmers will go out of business. A tells us that if the scientists are right, then some farmers will go out of business. A wrongly equates the scientists being right with their proposal being adopted. It is entirely possible the scientists are right, yet their proposal isn't adopted.
E doesn't make this mistake. It correctly notes that if the proposal is adopted farmers will go out of business, but adds in the caveat that they may not have to if they find other ways to increase their yields. This makes sense, if the only reason they would've gone bust was lower yields, they could avoid bankruptcy if they found another way to increase or preserve yields.
