A is the father of B, C is the son of A, D is the brother of E, E is the…

In a blood-relation puzzle, a person's uncle is the brother of one of their parents — never the parent, never a sibling, and never a grandparent. To find D's uncle, first build the family tree from the given statements, identify D's parent, and then find that parent's brother.

1. A is the father of B, so B's parent is A.

2. C is the son of A, so C and B are children of the same father — C is B's brother.

3. E is the daughter of B, so B is a parent of E; D is the brother of E, so D and E are siblings and D is also a child of B.

4. D's parent is B, and B's brother is C, so C — being the brother of D's parent — is the uncle of D.

Checking the generations confirms it: A is one generation above B and C (A is B and C's father), B and C are one generation above D and E (as parent and parent's sibling), so C sits exactly one generation above D as a parent's sibling — the definition of an uncle. A is too high (grandparent), B is D's own parent, and E is D's own peer, so none of them fit.

Hence, C is the uncle of D.