The most effective concessional sentence for the counter-argument is: "True, organic farms produce less food than GMO farms, but organic foods taste better and are less artificial than GMO foods."
This sentence is effective because it acknowledges the counter-argument that GMOs are more efficient than organic foods, but then goes on to point out that organic foods offer other important benefits. The sentence is also balanced and objective, and it avoids making any emotional appeals.
A. True, organic farms produce less food than GMO farms, but organic foods taste better and are less artificial than GMO foods.
This sentence is effective because it acknowledges the counter-argument that GMOs are more productive than organic foods, but then goes on to point out that organic foods offer other important benefits. However, the sentence could be improved by removing the phrase "less artificial," which is subjective and could be interpreted as an emotional appeal.
B. Obviously, GMOs are necessary in places with poor farmland, but in rich countries, farmers should be encouraged to grow organic foods.
This sentence is less effective than the others because it is less balanced and objective. The phrase "obviously" is dismissive of the counter-argument, and the phrase "should be encouraged" implies that the author is taking a side in the debate.
C. Organic farms do not produce as much food as GMO farms, so some nations populations will just have to tighten their belts a little.
This sentence is ineffective because it is dismissive and condescending. The phrase "just have to tighten their belts a little" is trivializing the issue of food security, and the sentence implies that the author is not concerned about the needs of people in developing countries.
The most effective concessional sentence for the counter-argument is the first one, which acknowledges the counter-argument but then points out the benefits of organic foods in a balanced and objective way.