The right answer is D.
The effectiveness of BT-Corn compared to conventional insecticide treatment is very much higher:
* The plant itself produces the toxin that blocks the digestion of or target insects: the entire plant is protected where a treatment (out of neonicotinoids, very expensive and reserved to the seed treatment) allows only a protection of surface and must be renewed several times.
* The selectivity of the treatment is very superior: each variant of the BT molecule targets only a family of insects but we do not know the impact of their cumulative effects in the environment.