Final answer:
The primary food source for flea larvae is dried blood excrement from adult fleas, also known as flea dirt.The correct option is b.
Step-by-step explanation:
The food of flea larvae is principally dried blood excrement from adult fleas. Unlike some other parasitic organisms that feed directly on the host's blood, flea larvae rely on the dried blood feces that adult fleas excrete after feeding on the host's blood. This is known as flea dirt and serves as the main food source for the developing larvae. Fleas are part of a larger group of animals known as ectoparasites, which live on the surface of their hosts during some or all stages of their life cycle and consume host-derived resources, such as blood, secretions, keratin, and skin cells.