The correct answer is A.
Prospero's attitudes toward both Ariel and Caliban are those of a master. His magic gives him power over them, and he wields it differently. He had rescued Ariel from a treen in which he had been trapped by Sycorax, a witch who was Caliban's mother, before Prospero's arrival in the island. Prospero constantly reminds Ariel of this fact, and promises him eventual liberation; this combination of guilt and hope keeps Ariel motivated.
Prospero's attitude towards Caliban is much harsher. Caliban views Prospero as a usurper, while Prospero thinks of Caliban as little more than a monster, and threatens him with pain to keep him in line. Caliban taught Prospero how to survive on the island, while Prospero taught him language and religion, while making him his servant.