Part 1:
The process that arrow C signifies is the burning of fossil fuels in order to present carbon dioxide into the atmosphere. The mentioned procedure in the carbon cycle is comparatively new as humans were not able to generate huge concentrations of carbon dioxide by burning fossil fuels until the emergence of the Industrial revolution.
Part 2:
The phenomenon, which could discharge the compound into the air is the burning of fuels. It is an oxidation reaction in which the carbon present in the hydrocarbons in the fuel is oxidized to carbon dioxide by the presence of oxygen in the air. The carbon dioxide discharged into the atmosphere contributes to the greenhouse effect.
Part 3:
The elements, which produce it are conserved at the time of the carbon cycle by the Law of Conservation of Matter. According to this law, the matter is neither consumed nor produced, it only gets transformed. So, at the time of chemical procedures in the carbon cycle, the atoms of carbon are never destructed, however, they get rearrange and modify into distinct molecules. The mentioned cycle is essential for maintaining life on Earth.