A is the daughter-in-law of C. B is the son of G. D is the brother-in-law of E. E is the grandmother of F. F is the only son of B. E has no siblings. H is the child of C and is not married. F is married. B has two children. There is no single parent in the family.

Which of the following pairs represents a married couple?

The correct option is Both [b] and [d].

To determine which pairs represent married couples, we can deduce the family tree step-by-step from the given statements:
1. Generation Structure:
- Statement: "E is the grandmother of F."
This places E in Generation 1 (grandparents), the parents of F in Generation 2, and F in Generation 3.
- Statement: "F is the only son of B" and "B is the son of G."
This means G is in Generation 1, B is in Generation 2, and F is in Generation 3.

2. First Generation Couples & Relatives:
- Since E is a grandmother in Generation 1 and G is a grandparent in Generation 1, G and E form a married couple: E – G (Option [d]).
- Statement: "D is the brother-in-law of E" and "E has no siblings."
Since E has no siblings, D must be the brother of E's husband (G). This confirms D is male.

3. Second Generation Couples & Children:
- B is the son of G and E.
- Statement: "There is no single parent in the family." Therefore, B must be married.
- Statement: "H is the child of C and is not married" and "A is the daughter-in-law of C."
This implies C is married to B. Together, B and C are the parents of F and H.
- Statement: "B has two children" and "F is the only son of B."
Hence, B's two children are F (son, male) and H (daughter, female).

4. Third Generation Couples:
- Statement: "F is married" and "A is the daughter-in-law of C."
Since F is the son of C, his wife must be A. Thus, A – F form a married couple (Option [b]).

Conclusion:
The married couples in the family are:
- G and E (E – G)
- B and C
- F and A (A – F)
Therefore, both pairs [b] (A – F) and [d] (E – G) represent married couples.