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

Correct — D.
Rule: grandfather or grandmother needs A's gender, and the statements never give it.

B is A's daughter, so A is B's parent.
D is the son of C, B's husband, and is read as B's son too.
So A is D's grandparent.

A could be a man or a woman, so grandfather and grandmother both fit → option (d).

Why the others are wrong

• (a)
  Father — Father is one generation off. A is B's parent and B is D's mother, so A sits two generations above D, not one.
• (b)
  Grandfather — Grandfather needs A to be male. The statements fix the genders of B, C and D but never A's, so nothing picks this over grandmother.
• (c)
  Grandmother — Grandmother needs A to be female, and no statement says so. Choosing it assumes a fact the question never gives.

Blood-relation chains are solved by drawing a small family tree: generations down the page, marriages across. Mark each person's gender only where a statement gives it.

Here the tree puts A two generations above D, so A is D's grandparent. The options offer grandfather and grandmother, and nothing in the question chooses between them, so the relation cannot be determined.

Key facts

• The statements fix B as female (daughter), C as male (husband) and D as male (son), and say nothing of A.
• A parent's parent is a grandparent: grandfather if male, grandmother if female.
• Choose 'Cannot be determined' when the statements leave two options equally possible, not merely when the chain is long.

Common traps

• Assuming A is male because nothing says otherwise
• Answering Father by reading 'B is the daughter of A' as A's relation to D

No directly related past PYQ was found.