❓ 题目 According to the passage, what is the main reason that the keystone species concept has been criticized?
- A. A. It is based solely on experiments with starfish in intertidal zones.
- B. B. The term is often used without sufficient evidence and its effects can vary by context.
- C. C. It overemphasizes the role of predators in controlling prey populations.
- D. D. It suggests that all species are equally important in an ecosystem.