❓ 문제 According to the passage, which of the following statements about keystone species is TRUE?
- A. A. Keystone species are always top predators that control prey populations.
- B. B. The concept of keystone species is universally applicable without any criticism.
- C. C. Keystone species can include non-predatory organisms such as ecosystem engineers.
- D. D. The impact of a keystone species is always proportional to its abundance.