TOEFL Listening: ETS-TOEFL听力机经 - 41MLUZ2YC0Z8W341P$

Which of the following is mentioned in the passage to imply that the use of tidal turbines hasn't been popular for a very long time? A. They have only been at the discussion stage of development. B. The ocean was too corrosive for the machines. C. They were too similar to windmills, which were not very reliable. D. The development of appropriate methods was severely insufficient.