___ research paper got a grade of A?

The correct choice is "whose" because it is the possessive form of "who," used to indicate that something belongs to or is related to someone. In this context, the research paper belongs to or is associated with a particular person, so using "whose" correctly conveys this relationship.

The other options do not fit contextually. "Who'se" is not a word in standard English. "Who is" is a phrase that implies a question or a statement about someone's identity but doesn’t indicate possession. "Who's" is a contraction of "who is" or "who has," which also does not express possession. Therefore, "whose" is the appropriate choice to indicate that the research paper in question is linked to someone.