Trophic levels are formed by-
D
organisms linked in food chain
Correct option is D. organisms linked in food chain
A trophic level is the position of an organism in a food chain. A food chain starts with producers which are green plants and occupy the lowest trophic level. The highest trophic level is occupied by carnivores which feed on lower trophic levels for energy. A simple food chain is represented as:
Plant ---> Herbivore ---> Carnivore
Hence, trophic levels are formed by different organisms linked in a food chain.
So, the correct answer is 'organisms linked in the food chain'.