C is A's father's nephew. D is A's cousin but not the brother of C. How is D related to C ?

Answer: Option B

C is A's father's nephew, means C is the son of A's father's brother i.e., C is the cousin of A. D is also A's cousin. So, D must be real brother or sister of C. But D is not brother of C. So, D must be sister of C.