A girl introduced a boy as the son of the daughter of the father of her uncle.…

Concept — A relation written as "the A of the B of the C of X" is resolved from the innermost person outwards: settle the last-named person first, then apply each preceding relation one link at a time, recording each new person’s generation level and gender on the family tree until the outermost relation is reached.

Application

1. Innermost person: “her uncle”. Take him as a brother of the girl’s mother, that is, her maternal uncle.

2. “The father of her uncle”: the father of that maternal uncle is the girl’s maternal grandfather.

3. “The daughter of the father of her uncle”: a daughter of that grandfather is a sister of the uncle, that is, the girl’s own mother.

4. “The son of the daughter of the father of her uncle”: a son of the girl’s mother is a male child of the same mother as the girl. That makes the boy her brother.

Cross-check

• Read the chain backwards to confirm it closes: her brother is a son of her mother; her mother is a daughter of her maternal grandfather; her maternal grandfather is the father of her uncle.

• Test the other reading of “uncle”: if he were her father’s brother, that father would be her paternal grandfather, his daughter would be the girl’s paternal aunt, and that aunt’s son would be the girl’s cousin, a relation the given choices do not contain. Only the maternal reading yields a relation that appears among the choices, so that is the intended reading.

The boy is therefore the girl’s brother.