(i) In a family of six persons A, B, C, D, E and F, there are two married couples. (ii) D is grandmother of A and mother of B. (iii) C is wife of B and mother of F. (iv) F is the grand daughter of E. Who among the following is one of the couples ?

C is wife of B. So, one couple is BC. Now, D in grandmother of A, B is the son of D and his wife C is the mother of F. SO, D is also the grandmother of F But F is the granddaughter of E. 

So, E is the grandfather of F and the husband of D. Thus, DF is another couple