Relationship Analysis:

Let's break down the given information to understand the family relationships and answer the questions.

Given Information:
- A is B's brother.
- C is A's mother.
- D is C's father.
- B is D's granddaughter.

Family Tree:

Based on the given information, we can construct the following family tree:

D
|
C
|
A
/ \
B

Relationships:

1. A is B's brother: This means A and B are siblings. A is a male.

2. C is A's mother: C is the mother of A. C is a female.

3. D is C's father: D is the father of C. D is a male.

4. B is D's granddaughter: B is the granddaughter of D. B is a female.

Analysis:

From the given information, we can conclude the following:

- B is the granddaughter of D, which means B is the child of D's child.
- A is B's brother, so A is also a child of D.
- C is the mother of A, so C is D's daughter.

Answering the Questions:

How is B related to D?
B is the granddaughter of D, which means B is D's granddaughter.

Who is A's son?
Based on the given information, A is not mentioned to have any children. Therefore, we cannot determine who A's son is with the provided information.

Summary:

From the given information, we can conclude that B is the granddaughter of D. However, we cannot determine who A's son is with the information given.

A is C's Son