Read this: Many organisms (of which humans are prime examples) eat from multiple levels of the food chain and, thus, make this classification problematic. A carnivore may eat both secondary and tertiary consumers, and its prey may itself be difficult to classify for similar reasons. Organisms showing both carnivory and herbivory are known as omnivores. Even herbivores such as the giant panda may supplement their diet with meat. Scavenging of carrion provides a significant part of the diet of some of the most fearsome predators. Carnivorous plants would be very difficult to fit into this classification, producing their own food but also digesting anything that they may trap. Organisms that eat detritivores or parasites would also be difficult to classify by such a scheme.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): From how many levels of the food chain do parasites usually eat?
unanswerable