Consider the following relationships among the members of a family of six persons A, B, C, D, E and F:
- The number of males equals that of females.
- A and E are sons of F.
- D is the mother of two, one boy and one girl.
- B is the son of A.
- There is only one married couple in the family at present.
Which one of the following inferences can be drawn from the above?