Which of the following is not a source of food for heterotrophs?

Heterotrophs are organisms that cannot produce their own food, and thus depend on other organisms for their nutritional requirements. They obtain their energy and nutrients by consuming other organisms or their products. Therefore, plants and animals are sources of food for heterotrophs. 

Some heterotrophs consume only plants, while others consume only animals, and still, others consume both plants and animals.

Sunlight is not a source of food for heterotrophs. Sunlight is a source of energy for autotrophs, which use it to synthesize organic molecules from inorganic raw materials, such as carbon dioxide and water. Heterotrophs cannot use sunlight directly as a source of energy or nutrients.