A is the sister of B. B is the son of C. C is married to D. D is the daughter…

Concept — Every sentence in a blood-relation chain fixes exactly one link between two people — either a descent link (child of / parent of) or a marriage link (spouse of) — and most of them also fix a gender. The relation asked for is then read off by resolving each person’s gender first and composing the links along the shortest path from one named person to the other, one step at a time.

Application — Take the given sentences in the order that resolves the genders fastest:

1. “E is the wife of F” makes E female and F male, and joins them as a married couple.

2. “D is the daughter of E” makes D female and places her one generation below that couple, so F is D’s father.

3. “C is married to D” joins C to D as her spouse, which makes C male.

4. “B is the son of C” places B one generation below the couple C and D, so D is B’s mother.

5. “A is the sister of B” makes A female and gives her the same parents as B, so D is A’s mother as well.

6. Composing the path from A: A → her mother D → D’s father F. That is two steps upward on the mother’s side, so F is A’s mother’s father — her maternal grandfather.

Cross-check — The one unused sentence, “G is the brother of D”, adds a sibling of A’s mother (A’s maternal uncle) but creates no shorter route between A and F, so the path A → D → F stands. Contrasting the other relationship terms against the same chain:

• “Father” would be C, the man married to D — one generation above A, not two.

• “Father’s brother” would be a male sibling of C; the only sibling named anywhere in the chain, G, is a brother of D and therefore sits on the mother’s side.

• “Wife’s father” describes F only as seen from C’s position, since F is the father of C’s wife D; from A’s position it is not the link being asked for.

Result — F is A’s mother’s father.