Textbook Problem

Which of the following is true about renewable natural resources?

1. a. They are a type of land resource (for example, oil, coal, and natural gas) that has a fixed stock.
2. b. They are a type of capital resource (for example, irrigation networks and wastewater treatment plants) that utilize water.
3. c. They are a type of capital resource (for example, air filtration systems in buildings) that renew and refresh polluted air from the outside.
4. d. They are a type of land resource (for example, forests, rangelands, and marine fisheries) that naturally regenerate and thus can tolerate a sustained harvest but can be depleted from excessive harvest.