Which of the following is an example of a primary consumer?

A primary consumer is an organism that primarily eats producers, such as plants and algae. In the context of the choices provided, a deer is a quintessential example of a primary consumer because it feeds on grass, leaves, and other vegetation. This plant-based diet places it squarely in the role of a primary consumer in the food chain.

Understanding the broader ecological context is crucial. While foxes, eagles, and bears are all part of the food web, they do not fit the definition of primary consumers as they primarily consume other animals or are omnivores that include both plant and animal matter in their diets. Thus, the deer, as a herbivore, stands out as the clear example of a primary consumer.