Family Structure Analysis

To determine which statement is true, we first need to establish the relationships and genders of the six family members based on the provided clues.

Summary of Deductions

• Couples: The two married couples are (D, E) in the first generation and (B, C) in the second generation.
• Family Tree: E (grandfather) and D (grandmother) are the parents of B (father). B is married to C (mother). A and F are their children.
• Genders:
  • Male: E, B
  • Female: D, C, F (F is a "granddaughter")
  • Unknown: The gender of A cannot be determined from the information given.

Evaluating the Statements

Now we can check the truthfulness of each option:

A. A is brother of F.

This statement can only be true if A is male. Since we do not know A's gender, we cannot confirm this is true.

B. A is sister of F.

This statement can only be true if A is female. Since we do not know A's gender, this also cannot be confirmed as true.

C. D has two grandsons.

D's grandchildren are A and F. We know F is a granddaughter (female). For D to have two grandsons, both A and F would need to be male. This is definitively false since F is female.

Conclusion

Since statements A and B are not necessarily true and statement C is definitively false, the correct option is that None of these statements are true.