The arrow C represents the emission of carbondioxide in the atmosphere. As you can see that the arrow is from the smoke that is emitted from the factories and industries and to the carbondioxide in the atmosphere.
The combustion process releases carbondioxide in the atmosphere. The combustion of fossil fuels releases carbon which is the underlying process representing arrow C
The arrow B represents the intake of carbondioxide by plants during photosynthesis to release oxygen
The arrow C represents the release of carbondioxide from industries due to the combustion of fossil fuels
The arrow D represents the dissolving of the carbondioxide into carbonates in the water bodies
Question 9:
The death and decay of the plants and animals that go underground converts the organic carbon in them into the inorganic form that forms fossils and fossil fuels. This process if indicated by the arrow E