A’s son B is married with C whose sister D is married to E the brother of B. How D is related to A?

The correct answer is C. Sister-in-law.

A’s son B is married with C. C’s sister D is married to E, the brother of B. This means that D is married to B’s brother. In law, a person’s brother’s wife is their sister-in-law.

Option A is incorrect because D is not A’s sister. Option B is incorrect because D is not A’s daughter-in-law. Option D is incorrect because D is not A’s cousin.