What is the professor's opinion about the future use of 2,4-D? A. She is convinced that 2,4-D will cause unintentional damage to crops. B. She is convinced that 2,4-D will be effective only for a limited period of time. C. She believes that 2,4-D will become too expensive for widespread use. D. She believes that 2,4-D will be most effective if combined with other herbicides.