M is the brother of N, B is also a brother of N, and M is the brother of D, but N is not a brother of D. In this situation, how is N related to D?

Introduction / Context:
This blood relation puzzle is designed to check whether you pay attention to gender clues hidden in statements like is not a brother. The logic is simple, but many students rush and miss the twist about N's gender, which completely changes the answer.

Given Data / Assumptions:

• M is the brother of N, so M is male and a sibling of N.
• B is also a brother of N, so B is another male sibling of N.
• M is the brother of D, so D is another sibling of M (and hence of N and B as well) in the same generation.
• N is explicitly stated to be not a brother of D.

Concept / Approach:
If M is brother of both N and D, then N and D are siblings too. The only issue is the gender of N. A person who is a sibling of D can be either a brother or a sister. The statement N is not a brother of D eliminates the brother possibility. Therefore, N must be a sister of D. The entire puzzle is basically about decoding that hidden gender information.

Step-by-Step Solution:
Step 1: From M is brother of N, note that N is a sibling of M.Step 2: From M is brother of D, we know D is also a sibling in the same family.Step 3: So M, N and D are siblings in one family group.Step 4: The puzzle says N is not a brother of D. In a sibling relationship there are two gender possibilities for N: brother or sister.Step 5: Since brother is ruled out, N must be D's sister.

Verification / Alternative check:
Imagine a family where parents have four children: M, N, B and D. The statement calls M and B brothers, and also calls M a brother of D. So M, B and D are clearly male siblings. When the question adds that N is not a brother, the only consistent way to keep N in the same sibling group is to treat N as female. That makes N the sister of D, which matches all the given clues.

Why Other Options Are Wrong:
Nephew and cousin imply different generations or different branches, but N is clearly a direct sibling of D.Brother is directly contradicted by the statement that N is not a brother of D.Aunt would belong to a generation above D, which the question does not indicate.

Common Pitfalls:
Many learners see words like brother repeatedly and unconsciously label everyone as male, ignoring the explicit phrase not a brother. Another mistake is thinking that not a brother means not a sibling at all, which is incorrect. The person can still be a sister. To avoid such errors, always separate generation (same or different) from gender and reason about each clearly.

Final Answer:
N is related to D as his Sister.