TOEFL Listening: TPO-TOEFL阅读TPO - 1ZK0BPL5824Q4ZP9N$

What conclusion does the author make in paragraph 3 about the effect of Bt plants on notarget organisms? A. Bt toxins do not affect nontarget organisms because the toxins only harm pests that eat the leaves, stems, or fruit of the plants. B. Bt plants have been shown in field studies to cause great harm to nontarget organisms. C. Bt plants do not cause as much harm to nontarget species as the use of conventional pesticides. D. Even if Bt toxins do not affect the insects that feed on the plants, they have harmful effects on birds that eat these insects.