Question 1: The relationship between the fungus and the ants is symbiotic. This is because both the ants and the fungus benefit from the interaction: the ants cultivate the fungus and feed on it, while the fungus gets a suitable environment to grow.
Question 2: The pair of organisms that can be in a parasite/host relationship is dogs and fleas. Fleas are parasites that live on dogs (the host) and derive benefits at the dog's expense.