Final answer:
The climax of "The Black Cat" is the protagonist's descent into madness.
Step-by-step explanation:
The climax of "The Black Cat" is A) The protagonist's descent into madness. This is the peak of the action, the main showdown, and the central event of the story where the conflict comes to a head.
Throughout the story, the protagonist's actions become increasingly disturbing as he becomes more consumed by his guilt. Ultimately, he reaches a point where he cannot control his violent impulses, leading to the climax of his descent into madness.