Final answer:
Carnivores obtain the carbon they need by eating primary consumers, which are herbivores that have consumed photosynthetic plants.
Step-by-step explanation:
Carnivores gain the carbon they need to survive by eating primary consumers. Primary consumers are herbivores that obtain energy by consuming plants or phytoplankton, which are able to convert light energy into food through the process of photosynthesis. In turn, carnivores consume these herbivores to obtain their needed nutrients. Therefore, carnivores are considered secondary or tertiary consumers in food chains and gain carbon from the organic matter of the organisms they eat, which originally came from photosynthetic organisms.