The most accurate answer to how carbon stored in the bodies of living organisms moves into rocks is:
b. living organisms decay and become fossil fuels, which eventually become rocks.
This process involves the accumulation of organic material from living organisms, which, over millions of years and under specific conditions, gets transformed into fossil fuels (like coal, oil, and natural gas). These fossil fuels can eventually become part of sedimentary rock formations. Other options have elements of truth regarding carbon cycling, but they do not specifically address the transformation of carbon from living organisms into solid rock through fossilization.