Analyzing Statement I: D's Children

Statement I says: "D is married to A and has three children."

• This statement tells us the total number of children D has is 3.
• However, it does not specify the gender of these children.
• The children could be any combination of sons and daughters (e.g., 3 sons, 2 sons and 1 daughter, 1 son and 2 daughters, or 0 sons and 3 daughters).
• Therefore, Statement I alone is not sufficient to determine how many sons D has.

Analyzing Statement II: B's Children

Statement II says: "B is A's brother and has three sons."

• This statement provides information about B's children, specifically that B has 3 sons.
• The question asks about the number of sons D has.
• The fact that B (A's brother) has sons does not give us any information about D's children, even though D is married to A. The children belong to B, not D.
• Therefore, Statement II alone is not sufficient to answer the question.

Analyzing Both Statements Together

Now, let's consider both statements together:

• Statement I: D has 3 children.
• Statement II: B has 3 sons.
• Combining these pieces of information, we know D has 3 children in total, and B has 3 sons.
• There is no information linking B's sons to D's children. We still don't know the genders of D's three children.
• Knowing that D's spouse's (A's) brother has sons doesn't tell us how many sons D has.
• Therefore, even with both statements, we cannot determine the number of sons D has.

Conclusion

Since neither statement alone nor both statements combined provide enough information to answer the question "How many sons does D have?", the correct option is that both statements together are not sufficient.