❓ 题目 According to the passage, which of the following statements about keystone species is true?
- A. A) Keystone species are always the most abundant organisms in an ecosystem.
- B. B) Robert Paine's experiment showed that removing a predator can increase biodiversity.
- C. C) The concept has been applied only to predators and not to other functional roles.
- D. D) The importance of a keystone species may vary depending on the ecological context.