The correct option is
C Omnivore
A. A herbivore is a primary consumer that depends upon producers for its food.
B. A carnivore is a secondary consumer that depends on herbivores (primary consumer) and producers for its food.
C. An omnivore is a tertiary consumer that depends on herbivores (primary consumers), carnivores (secondary consumers) and producers for its food.
D. An autotroph is a living organism that can prepare its own food. For example, green plants.
E. Detritivores are a type of consumers which depend on organic detritus. For example, earthworm breakdown detritus into smaller particles.
Hence, the organism that eats both plants and animals is an omnivore.
So, the correct answer is 'Omnivore'.