The correct answer is option D.
The U.S have been planting genetically modified crops. These crops have benefits more than normal crops but there could be some possible negative sides of these crops.
There could be longer term problems associated with the production of the genetically modified crops and these negative effects can be non predictable.
There are many predictable reasons associated with the use of genetically modified crops that can be cured but some of the results might have unforeseen impact on the environment.