I would say A. Either tall or short
When Mendel crossed purebred short plants with purebred tall plants, all of the offspring were TALL
The pure-bred tall plant dominated the short
A downside to this mutant corn wohld be that it would give rise to a presticide-immune strain of the certain insect.
All the non-immune bugs would die, leaving the few immune ones to reproduce. That would result in a overpopulation of immune super-bug that would still be able to go ham on the large, GMO corn, like nothing happened, and still go on to affect native plant populations. That can become a huge problem.
Hope that helped!