D. Mom should be capitalized because I believe it is a proper noun.
You can replace the word mom with a person's name. That is not always the case however. For example, I called my mom on my.... If you capitalized mom in this sentence and put a name then it wouldn't make sense because the word my was added. Hopefully this helps and makes sense. Good luck!!!
The House is an example of symbolism. By trying to hide the dead body of the old man from the policemen under the floorboard. The narrator is symbolically trying to hide the guilt and shame of his crime in his subconscious.
