A Farmer Uses Triazine Herbicide to Control Pigweed in His

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; however, after several years, the farmer sees more and more pigweed growing once again in the fields. Which of the following statements best explains the return of pigweed to the farmer's fields?

A) The herbicide company 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 photosynthetic pathways than the original form.
D) Triazine-resistant weeds were more likely to survive and reproduce than were non-resistant individuals.