I presume you have these lines in mind:
"CALIBAN (kneeling): As I told thee before, I am subject to a tyrant, a sorcerer that by his cunning hath cheated me of the island."
The correct answer is B: He is enslaved by a tyrant. He then explains that his tyrant (Prospero) has cunningly deceived him and took his island from him. Caliban wants Trinculo and Stefano to help him murder Prospero and retrieve the island.