A relative pronoun is used after a noun to help identify which person or thing we are talking about or to tell us some more information about a person or thing.
Here is list of pronouns - who, which, that, whose, whom.
e.g. I saw the old book which was hidden in the upper shelf.
book is the noun and which is the relative pronoun.
the relative pronoun which is used to refer to things and animals.
So, the correct answer is option
A) Relative pronoun - which; Antecedent - resignation papers