There are six children playing football namely A, B, C, D, E and F.
A and E are brothers. F is the sister of E. C is the only son of A's uncle.
B and D are the daughters of the brother of C's father.
How is D related to A ?
Clearly, D's father is the brother of C's father and C's father is A's uncle.
So, D's father is also A's uncle.
Thus, D is A's Cousin.
Hence, the answer is (d).