Pointing to a man in a photograph, a woman says, "He is the only son of the only daughter-in-law of my only son's father." How is the man related to the woman?

Answer: B. Grandson

"My only son's father" is the woman's husband.
The "daughter-in-law of her husband" is her own daughter-in-law (the wife of her son).
The "only son" of her daughter-in-law is the woman's grandson.

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