a) On this question you have to explain the rol of the components of the food web that are asked, in ohter words, what they consume and if they are consumed. Keep in mind that the popoulation of a specie affects the population of its consumers and prey.
Scavengers are animals that feed from dead organic material or carrion.
Decomposers are the organisms that help decompose dead organic material, (not only the organism but its secretions too) usually found at the end of the food chain.
Parasites need another organisms to be their host, which provides them with food and/or shelter. They benefit from the host by affecting it negatively.
b) Search for information, or what you have been provided in class and give two examples of food chains that include the arctic hare.