The right option is; a. Predation and commensalism
Predation is an interaction between organisms in which one organism (the predator) benefits from another organism (the prey), while commensalism is also an interaction between organisms of different species in which one species benefits from the other without either harming or benefiting the latter. From the question, the remoras benefits from the relationship by living on sharks and feeding on the leftovers of the sharks, but the sharks are not affected in any way. The relationship describes predation and commensalism.