A is the daughter of B. B is the son of C. D is the wife of C. How is D related to A?

Correct — C.
Rule: climb one generation at a time, starting from A.

A is the daughter of B, so B is A's parent.
B is the son of C, so C is A's grandfather (C is male: D is his wife).
D is C's wife, so D is B's mother and A's grandmother → option (c).

Why the others are wrong

• (a)
  Aunt — An aunt is a parent's sister or an uncle's wife. D is married to C, A's grandfather, so she sits two generations above A, not one.
• (b)
  Mother — A's mother would be B's wife. D is the wife of C, B's father, which puts her a generation higher, as B's mother.
• (d)
  Sister — A sister shares A's parent, B. D is married to A's grandfather, so she belongs to A's grandparents' generation.

Blood-relation chains are solved one link at a time, starting from the person the question asks about.

Fix each person's generation and gender as you go. B is male (a son), C is male (D is his wife), and D is female.

Two links separate A from C: A → B → C. D joins C's generation by marriage, so she is A's grandmother.

Key facts

• A father's mother is a paternal grandmother.
• "D is the wife of C" fixes C as male and D as female.
• A → B → C spans two generations, so C is A's grandfather.

Common traps

• Answering Mother by stopping one link short, at B's wife
• Taking D for an aunt because she married into the family

No directly related past PYQ was found.