D says: “A's father is the only brother of my sister's son.” Based on this statement, determine how A's father is related to D. Choose the most precise relationship from the options.

Introduction / Context:
Blood-relation puzzles often compress multiple family links into a short sentence. The task is to translate the English into a clear kinship chain and then read off the exact relationship asked. Here, D says “A’s father is the only brother of my sister’s son.” We must identify how A’s father relates to D. Because everyday family terms can be ambiguous if read casually, we will decode terms carefully and verify the result against alternatives.

Given Data / Assumptions:

• Speaker is D.
• D has a sister.
• D’s sister has a son (this person is D’s nephew).
• That nephew has an “only brother,” and that “only brother” is A’s father.
• All relations are within a standard, monogamous family context; no step/adoptive exceptions unless stated.

Concept / Approach:
Translate each phrase into a kinship arrow. “My sister’s son” points to D’s nephew. “Only brother of my sister’s son” means we are looking at this nephew’s brother, i.e., the other son of D’s sister. If D’s sister has two sons, those two are brothers to each other. One of them is explicitly called D’s sister’s son; the other is “the only brother” of that son. That “only brother” is identified as A’s father.

Step-by-Step Solution:

Verification / Alternative check:
If A’s father were D’s cousin or uncle, the chain would have to pass through D’s parents or grandparents, but the sentence anchors everything to “my sister’s son,” locking the relation to D’s sister’s children. Hence “nephew” is uniquely determined.

Why Other Options Are Wrong:

• Cousin: Cousins share grandparents with D; here the link runs through D’s sister’s child, not a sibling of D’s parent.
• Aunt: “Aunt” is female and generationally above or lateral from D; A’s father is male and below D’s sister.
• Data inadequate: The sentence is sufficient; no ambiguity remains after parsing.
• None of these: Not needed because “Nephew” fits perfectly.

Common Pitfalls:

• Misreading “my sister’s son” as “my sister-in-law’s son.” It explicitly says “my sister.”
• Assuming “only brother” could be the same person; the phrase contrasts two distinct sons.

Final Answer:

Nephew