Q. 5. Which statement best explains why the carbon cycle is classified as a closed-loop system?
answer choices
A. Carbon levels are monitored and maintained by
plants in a system.
B. The flow of carbon occurs only in nonliving
components of a system.
C. Earth's atmosphere traps all carbon once it
passes through living organisms in a system.
D. A fixed amount of carbon flows between the
living and nonliving components of a system.