The answer is C. It may affect non-target organisms.
You can cross-out A, as for sure before applying such a modifications, it is tested if it is harmful to humans or not.
Also B and D are not major problems to consider.
Also E is totally wrong.
While C, is the most critical one as even if scientists tested the effect on the mutualistic organisms found in the soil, they can't test it on all the organisms that will really interact with the plant! They cannot predict all the outcomes.
Hope this helps!
