In Relation puzzle type, mutual blood relations or other information of more than two persons are mentioned and information about any two is mentioned.
A and B are brothers. C and D are sisters. A's son is D's brother.
How is B related to C ?
Clearly, B is the brother of A; A's son is D's brother. This means D is the daughter of A.
Since C and D are sister, C is also the daughter of A.
So, B is the uncle of C.
Hence, the answer is (d).