What is Lisa's relationship to Dennis, if she stated "he is the only son of my mother's mother"?

The correct answer indicates that Lisa is Dennis's niece because she describes him as "the only son of my mother's mother." To break this down, Lisa's mother's mother is Lisa's grandmother. The phrase implies that Dennis is the only son of Lisa's grandmother, which would make him Lisa's uncle (if we only considered direct lineage). However, there’s a contextual component that defines Lisa as his niece. Since the question directly depicts a familial relationship, the positioning suggests that Lisa is referring to family structure through the lens of her being a descendant (in this case, the daughter of one of the siblings of Dennis).

This wording makes it clear that Lisa is a child whose mother is a sibling of Dennis's mother (making Dennis an uncle) while also placing Lisa in the role of niece in relation to her uncle, thus clarifying her relationship to him. The notion of being a niece confirms her place in the generational family tree relative to Dennis. Other options like mother, cousin, or aunt do not accurately describe the relationship based on the familial clues given in the statement.