The correct answer is E. Nephew.
The boy is the son of the daughter of the father of the girl’s uncle. This means that the boy is the grandson of the girl’s great-uncle. The girl’s great-uncle is her uncle’s father. Therefore, the boy is the girl’s nephew.
Here is a diagram of the family tree to help illustrate the relationship:
[Diagram of a family tree with the girl, her uncle, her great-uncle, and the boy]
The girl is represented by the green circle. Her uncle is represented by the blue circle. Her great-uncle is represented by the red circle. The boy is represented by the yellow circle.
As you can see, the boy is the son of the girl’s great-uncle’s daughter. This makes him the girl’s nephew.
The other options are incorrect because they do not accurately reflect the relationship between the girl and the boy.
Option A is incorrect because the boy is not the girl’s brother. The boy is the son of the girl’s great-uncle’s daughter. This makes him the girl’s nephew, not her brother.
Option B is incorrect because the boy is not the girl’s son. The boy is the son of the girl’s great-uncle’s daughter. This makes him the girl’s nephew, not her son.
Option C is incorrect because the boy is not the girl’s uncle. The boy is the son of the girl’s great-uncle’s daughter. This makes him the girl’s nephew, not her uncle.
Option D is incorrect because the boy is not the girl’s son-in-law. The boy is the son of the girl’s great-uncle’s daughter. This makes him the girl’s nephew, not her son-in-law.