In a family of six members , A is husband of B. C is B's sister, and D is C's father. F is D's mother. How is F related to A?

Given: In a family of six members , A is husband of B.

C is B's sister, and D is C's father.

F is D's mother. 

From the given information relationship diagram will be

 F is  Grandmother-in-law of A

Thus, correct option is (a).