Plants transfer carbon in the carbon cycle a. through assimilation of carbon from the soil. b. through fixation of carbon in the soil c. when carbon transpires from their stomatae d. when they are eaten by animals.

 The correct answer is D. when they are eaten by animals.
 Carbon cycle includes movement of CO2 from the atmosphere, through various organisms, then back into the atmosphere again. Plants (or algae or bacteria) use atmospheric CO2 from the atmosphere, to generate oxygen through the process of photosynthesis. The carbon then becomes part of molecules like proteins, fats and carbohydrates. Passing carbon from one organism to the next occurs when an animal eats a plant or when microorganisms and some animals feed on waste material from animals or dead animals and plants (detritus feeders). CO2 gets back to the atmosphere by respiration of animals, plants, algae and microorganisms. It can also be released into the atmosphere when fossil fuels are burned.