A farmer uses triazine herbicide to control pigweed in his field. For the first few years, the triazine works well and almost all the pigweed dies; but after several years, the farmer sees more and more pigweed. Which of these statements explains why the pigweed re-appeared?A) Natural selection caused the pigweed to mutate, creating a new triazine-resistant species. B) The herbicide company lost its triazine formula and started selling poor-quality triazine. C) Triazine-resistant pigweed has less efficient photosynthesis metabolism. D) Only triazine-resistant weeds survived and reproduced, so each year more pigweed was triazine-resistant.