The term "primary producer" is used to describe organisms that can produce their own energy without feeding on others, this includes plants and algae that produce food and energy through photosynthesis using light and other inorganic compounds. Additionally, the primary producers can be identified because in ecosystems they are always on the first level and they are eaten by others.
According to this, the one that is a primary producer is an oak tree because this is a type of plant and therefore can produce its food through photosynthesis different to others that need to feed on other organisms to obtain energy.
