22. 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 explanations best explains what happened? (A) The herbicide company lost its triazine formula and started selling poor-quality triazine. (B) Natural selection caused the pigweed to mutate, creating a new triazine-resistant species. (C) Triazine-resistant pigweed has less-efficient photosynthesis metabolism. (D) Triazine-resistant weeds were more likely to survive and reproduce.