A is the brother of B, who is the sister of C. A, B and C are the children of E and F. How is F related to B?
Which of the below information is additionally required to answer the above question?​​

Given: 

A is the brother of B, who is the sister of C.

A, B and C are the children of E and F.

We have no information about the gender of E and F.

Now, we check each options.

Option (a):C is the son of F

No information about the gender of C.

Option (b):E is the father of A.

So, option b is sufficient for answer the question F is the mother of C.

Thus, correct option is (b).