When usher decides to preserve his sister’s body for two weeks in the vault in the house, why does the narrator go along with the idea?

a. he suspects that madeline is not truly deceased yet.
b. he knows that usher will go insane if madeline’s body leaves the house.
c. he understands that usher wants to keep madeline’s body away from the physicians.
d. he understands that using the vault has been a family tradition.