In case ofwhich one of the following biogeochemical cycles, the weathering of rocks is the main source of release of nutrient to enter the cycle?

1. A

   Carbon cycle

   Carbon. Atmosphere and photosynthesis, not rock weathering as the main entry.

2. B

   Nitrogen cycle

   Nitrogen. Atmosphere + fixation.

3. C

   Phosphorus cycle

   Phosphorus. No gaseous stock; weathering of phosphate rock feeds the cycle.

4. D

   Sulphur cycle

   Sulphur. Atmosphere and volcanoes as well as rock.

Summary. Official key is (c) phosphorus. The phosphorus cycle is sedimentary: weathering of rocks is the main natural input. C, N and S have large air pathways.