The answer should be C, carnivores that feeds on secondary consumers.
A basic food chain basically contains a producer, a primary consumer, a secondary consumer, and a tertiary consumer. Any consumers above tertiary consumers are still called tertiary consumers. The sun and the decomposes are not listed in a food chain. A food web is just a lot of food chains combined together.
A producer is a plant that makes energy from the light energy of sun. They do this by photosynthesis. Only plants can use sun as their energy source. Animals cannot photosynthesize.
A primary consumer is an animal that consumes the producer. It wouldn't be a plant because plants can't consume plants. Any animals that consume plants for their energy are called herbivores.
A secondary consumer is an animal that consumes the primary consumer. They're also animals, as plants can't consume animals. Any animals that consume another animal for their energy source are called carnivores.
A tertiary consumer is basically very similar to secondary. Again, must be an animal. They feed on the secondary consumer in a food chain. Since the secondary consumer is an animal, so they're called carnivores.
Therefore, your answer is carnivores that feeds on secondary consumers.