❓ 题目 According to the passage, which of the following statements about the keystone species concept is TRUE?
- A. A. The concept was first proposed based on observations of terrestrial ecosystems.
- B. B. Removing a keystone species always leads to the extinction of all other species in the community.
- C. C. The effect of a keystone species can vary depending on environmental conditions and other species present.
- D. D. Keystone species are always predators or ecosystem engineers.