❓ 문제 According to the passage, what is a primary reason that ecosystem services are often undervalued in economic terms?
- A. A. They are difficult to quantify because they are not bought and sold in markets.
- B. B. They are primarily cultural benefits that have no direct monetary value.
- C. C. They are public goods, leading to a 'tragedy of the commons' that depletes them.
- D. D. They have only been studied in the last two decades, so data is limited.