Answer:
The correct answer would be a. autotrophs.
Autotrophs, also called producers are the organisms which are able to produce complex organic compounds such as fats, proteins and carbohydrates from simpler substances present in the environment.
They are of two types based on their source of energy:
Photoautotrophs: These are the organisms which use sunlight as the source of energy in order to produce organic compounds.
For example, green plants synthesize their own food (glucose) from carbon dioxide with the help of sunlight and chlorophyll. Oxygen is released as the byproduct. The overall process is termed as photosynthesis (photo meaning photon or light energy).
Chemoautotrophs: They get energy from electron donor compounds such as sulfur, hydrogen sulfide et cetera.