|A) Teacher||B) Doctor|
|C) Lawyer||D) None of these|
C is the daughter-in-law of A who is the grandmother of F means C is the mother of F But F is the son of B.
So, B is C's husband. But C, the lawyer is married to the Doctor So, B is the Doctor. F, the Accountant, will be the son of B and C, E is the unmarried Engineer.
So, the other named couple can be that of grandmother of F. i.e, A and D But D, the Salesman, is married to the Lady Teacher. So, D, the Salesman, is the grandfather of F, father of B and the husband of A, the Lady Teacher.
Clearly, B is the Doctor.