Answer: c.ununtterable loathing
Explanation: The context clue that best helps to clarify the meaning of the word "odious" in this sentence from "The Black Cat", by Edgar Allan Poe, is unutterable loathing. The narrator used to love Pluto, the black cat. But the cat's fondness for him makes him dislike it. This feeling begins to increase and it becomes hatred. Unutterable means that can not be expressed with words. Loathing means a strong feeling of hatred. These words help clarify the meaning of the word "odious".