Final answer:
The relationship between a tapeworm and a cat is a parasitic one, where the tapeworm benefits at the expense of the cat's health.
Step-by-step explanation:
A tapeworm and a cat have a parasitic relationship. Parasitism is a type of symbiotic relationship in which one species, the parasite, benefits at the expense of another, the host. In this case, the tapeworm lives inside the cat, deriving its nutrients from the cat's body, which can cause harm to the cat.
Unlike commensalism, where one organism benefits and the other is unaffected, parasitism negatively affects the host. Therefore, among the given options, parasitism is the correct answer to describe the relationship between a tapeworm and a cat.