How do autotrophs mainly obtain energy?

Autotrophs are organisms that are capable of producing their own food from inorganic materials, primarily using energy sources like sunlight or chemical reactions. The most common method for autotrophs to obtain energy is through photosynthesis, a process in which they convert sunlight into chemical energy to synthesize glucose and other carbohydrates from carbon dioxide and water. This process not only provides energy for the autotroph itself but also releases oxygen as a byproduct, which is crucial for life on Earth.

In addition to photosynthesis, some autotrophs utilize chemosynthesis, where they derive energy from the oxidation of inorganic substances, but this is less common among the majority of autotrophs typically studied. Therefore, the main characteristic that distinguishes autotrophs is their ability to create their own organic compounds and energy from inorganic sources, making option C the correct answer.