Pointing to a woman, John says, “She is the wife of my uncle’s only son.” How is the woman related to John?

Correct — C. Rule: decode the chain one link at a time, from John outwards.

John's uncle's only son is John's cousin.

The woman is that cousin's wife, so she is related to John by marriage, in his own generation.

Sister and Cousin are blood relations, and Niece is a generation below John. Sister-in-law is the option that names a relative by marriage in his generation — option (c).

Why the others are wrong

• (a)
  Sister — A sister shares John's parents. This woman is linked to John through her marriage to his cousin, so she is no blood relative of his.
• (b)
  Cousin — John's cousin is her husband, the uncle's son. She married into the family, so she is the cousin's wife, not a cousin by blood.
• (d)
  Niece — A niece is a sibling's daughter, one generation below John. The woman is married to John's cousin, who is in John's own generation.

Chain relations are decoded one link at a time, starting from the speaker. "My uncle's son" is my cousin, and "only" simply fixes which son is meant.

The last link, wife of, is a marriage link. It keeps the generation the same and turns a blood relation into a relation by marriage.

So the woman stands in John's generation and is related to him through marriage.

Key facts

• An uncle's son is a first cousin.
• Dictionaries define sister-in-law as a spouse's sister, a brother's wife or a spouse's brother's wife.
• A wife-of link keeps the generation and turns a blood relation into a relation by marriage.

Common traps

• Choosing Cousin because the husband is John's cousin, and dropping the wife-of link.
• Choosing Niece by placing the uncle's son a generation below John.

No directly related past PYQ was found.