A’s father’s wife’s only daughter is B. How is A related to B?

Correct — C.
Rule: father's wife = mother, the standard reading in blood relations.

A's father's wife is A's mother. Her only daughter is B, so A and B are children of the same parents.

B is the only daughter, so A is not a daughter: A is B's brother, which the options word as Sibling → option (c).

Why the others are wrong

• (a)
  Nephew — Nephew is a sibling's son, one generation below. A and B are children of the same mother, so they stand in the same generation.
• (b)
  Cousin — Cousin means sharing grandparents but not parents. A and B share a mother, A's father's wife, so they are closer than cousins.
• (d)
  Uncle — Uncle is a parent's brother, one generation above. Nothing puts A above B: both are children of the same couple.

Chained possessives are read from the inside out: A's father, then that man's wife, then her only daughter. Each step lands on a person you can place in a family tree.

A's father's wife is A's mother, so the chain ends at A's sister. The word only does extra work: it rules out A being a daughter, which makes A the brother.

Key facts

• Father's wife and mother's husband are read as one's own mother and father.
• 'Only daughter' means no other daughter exists, so any other child of that mother is a son.
• Siblings share parents. Cousins share grandparents but not parents.

Common traps

• Reading 'only daughter' as a hint that A is female, when it rules that out
• Answering Cousin because the chain passes through the father's wife, as if she belonged to another family

No directly related past PYQ was found.