TOEFL Listening: ETS-TOEFL听力机经 - 9D446QF0D8NMFP_VP$

What does the professor say about the corn and soybean plants that were used in the experiment? A. They were treated with 2,4-D in fields, but not in greenhouses. B. They were less productive than the researchers had expected them to be. C. They were manipulated to produce protective bacterial enzymes. D. They were selected for the experiment because they are more easily damaged by 2,4-D than by glyphosate.