Which of the following is NOT a limitation to using auxotrophs to prevent the spread of genetically modified genes to wild populations?

A) Auxotrophs may mutate in ways that allow them to synthesize the limiting nutrient.
B) Auxotrophs self-destruct using self-toxins when this method is applied.
C) Auxotrophs often cross-feed from the metabolites of other organisms in the environment.
D) Back mutation to the wild type may occur.