(i)M is the brother of N
(ii) B is the brother of N,and
(iii)M is the brother of D, which of the following statements is definitely true?

Options

A. N is the brother of B
B. N is the brother of D
C. M is the brother of B
D. D is the brother of M

Explanation

To solve the problem step by step, we will analyze the relationships given in the statements and determine which conclusion can be drawn definitively.

### Step 1: Analyze the statements
1. **M is the brother of N**: This tells us that M is male (brother) and N can be either male or female.
2. **B is the brother of N**: This tells us that B is also male (brother) and reinforces that N can be either male or female.
3. **M is the brother of D**: This tells us that M is male, and we do not know the gender of D.

### Step 2: Establish relationships
- From the first statement, we know:
- M (male) - N (unknown gender)

- From the second statement, we know:
- B (male) - N (unknown gender)

- From the third statement, we know:
- M (male) - D (unknown gender)

### Step 3: Determine the relationships
- Since M and B are both brothers of N, they are brothers to each other:
- M (brother) - B (brother)

- The gender of N is still unknown, so we cannot conclude anything about N's relationship with D or B definitively.

### Step 4: Evaluate the options
1. **N is the brother of B**: This cannot be concluded because N's gender is unknown.
2. **N is the brother of D**: This cannot be concluded because N's gender is unknown.
3. **M is the brother of B**: This is definitely true because both M and B are stated to be brothers.
4. **D is the brother of M**: This cannot be concluded because we do not know D's gender.

### Conclusion
The only statement that is definitely true is:
- **M is the brother of B**.

Thus, the correct answer is option 3.