❓ 質問 According to the passage, why is the keystone species concept considered controversial?
- A. A. It is difficult to apply because many species have strong effects only under certain conditions.
- B. B. It has been proven to be ineffective in predicting ecosystem changes.
- C. C. It relies too heavily on experiments with starfish that are not representative.
- D. D. It is only useful for marine ecosystems, not terrestrial ones.