TOEFL Listening: ETS-TOEFL听力机经 - 91MP4F3K29YK8DY1P$

What is the professor's opinion about the environmental impact of tidal turbines? A. They can cause significant harm to marine life. B. They can provide enough energy to offset any negative effect on the environment. C. They have almost no effect on marine life, due to recent technological advances. D. They have some effect on the environment, but that effect is still unknown.