Answer: A. Some of the puzzle pieces are missing.
Explanation: "A pronoun that does not refer to any person, amount, or thing in particular." That is the definition of an indefinite pronoun. I also looked at examples and a list of pronouns and that was on there, so I am pretty sure A is the answer.
No, he is not able to stop the madness that destroys Usher.
Madeline comes out from where they've buried her alive covered with the blood of her struggles and attacks Roderick. The effort drains whatever life she had left and she dies. Roderick dies from the shock of it all. The narrator flees the house just as it begins to crumble like it's inhabitants - because really they're one in the same.