Which of the following statements about biogeochemical cycles is true?
a. biogeochemical cycles are cycles involving only nonliving components.
b. the rock cycle is a biogeochemical cycle.
c. biogeochemical cycles are not an important part of the earth system.
d. carbon, nitrogen, and oxygen cycles are biogeochemical cycles.

Letter D. is the answer. Carbon, nitrogen, and oxygen cycles are bio-geochemical cycles.
Biogeochemical cycle or cycling of substances or substance turnover is a pathway by which a chemical substance moves through biotic and abiotic compartments of the Earth: lithosphere, atmosphere, and hydrosphere. The term biogeochemical tells that biological (bio) and geological (geo) and chemical factors are all involved. The circulation of chemical nutrients such as carbon, nitrogen, oxygen, phosphorus, calcium and water by biological and physical world constitute the biogeochemical cycles. As an effect, the element is recycled, although in some cycles there may be reservoirs where the element is accumulated/ held for a long period like ocean or lake for water.

Where are the following choices