From an ecological perspective, who rules the world? plants b herbivores c carnivores d decomposers

From an ecological perspective, A. plants rule the world.

Though herbivores, carnivores, and decomposers are all at higher points on the food chain than plants, these organisms all must rely on other organisms for energy. Plants are the only organisms that produce their own energy; therefore, they rule the world. All organisms energy is sourced back to plants because plants are basically the "creator of all energy," for they produce their own energy through photosynthesis.  

Hope this helps! :)