passage
An increase in human-made carbon dioxide in the atmosphere could initiate a chain reaction between plants and microorganisms that would unsettle one of the largest carbon reservoirs on the planet–soil. In a study, it was found that the soil, which contains twice the amount of carbon present in all plants and Earth’s atmosphere combined, could become increasingly volatile as people add more carbon dioxide to the atmosphere. This is largely because of increased plant growth. Although a greenhouse gas and a pollutant, carbon dioxide also supports plant growth. As trees and other vegetation flourish in a carbon dioxide-rich future, their roots could stimulate microbial activity in soil that may in turn accelerate the decomposition of soil carbon and its release into the atmosphere as carbon dioxide.
Which among the following is the most logical corollary to the above passage,
(a) Carbon dioxide is essential for the survival of microorganisms and plants
(b) Humans are solely responsible for the release of carbon dioxide into the atmosphere
(c) Microorganisms and soil carbon are mainly responsible for the increased plant growth
(d) Increasing green cover could trigger the release of carbon trapped in soil