Answer:
D. Primary consumer
Step-by-step explanation:
In an ecosystem, organisms tend to feed on one another in order to derive energy needed for their life processes. This feeding pattern is termed FOOD CHAIN in Ecology. Every food chain is usually started by a unique set of organisms called PRODUCERS. Producers are autotrophic organisms e.g plants, capable of producing their own food via the use of sunlight in a process called PHOTOSYNTHESIS.
A group of organisms called HETEROTROPHS, however, cannot produce their own food. Hence, they depend on other animals. In a food chain, animals that fall into this category are called CONSUMERS. Consumers feed on other organisms to derive their energy. Consumers that feed directly on the producers (plants) are called PRIMARY CONSUMERS. This is the case of a white-tailed deer feeding on leaves and grasses, which are plant producers, in an ECOSYSTEM. This white-tailed is said to be a PRIMARY CONSUMER as it feeds directly on plants (producers).