Which event belongs in the missing box in the timeline above?

Ithink the answer is either a , c or d

Genetically modified corn is a very controversial issue because of the potential benefits that it can bring, but also the potential for it to bring problems in the future. genetically modified corn can be beneficial in the developing world because it can be modified to be resistant to drought, or pesticide, and therefore the crop is stronger and easier to grow. however, the use of gmo corn can also be problematic because they decrease the diversity in the types of seeds that are used to grow food and also can make farmers dependent on the seeds from companies because they can only be used once to grow corn.