❓ 题目 According to the passage, what is a major difficulty in valuing ecosystem services?
- A. A) They are not traded in markets, making their economic contribution invisible.
- B. B) Their provision can change abruptly when environmental thresholds are crossed.
- C. C) Critics argue that monetizing nature ignores its intrinsic value.
- D. D) Mangrove forests are often cleared for aquaculture, reducing their protective function.