The correct option is
E Prey
A. Producers are the green plants that convert solar radiations into chemical energy. They are the photosynthetic plants and their kind varies with the kind of the ecosystem. For example, in a dense forest, the tress are the producers, in lakes and ponds, the rooted or large floating plants and microscopic plants (phytoplankton) are the producers.
B. Predator is the organism that feeds on others for its food.
C. Host is an organism that harbours another organism. It may be a plant , animal, parasite, symbiont etc.
D. Scavenger is an organism that has the feeding behaviour of both herbivores and carnivores. It feeds on the dead plant and animal material which is present in its habitat.
E. Prey is an organism that is eaten by another organism, the predator.
Hence, if red-tailed hawk hunts, kills and eats a squirrel, then the hawk will be a predator and the squirrel will be the prey for hawk.
So, the correct answer is 'Prey'.