D.)father. Since Suresh's mom has only one son and the boy in the picture is the son of the only son Suresh's mother have ,the relationship between the boy and Suresh is of father and son.So Suresh is the father.
The correct option is D. The mother has only one son. And the boy in the photograph is the son of the only son. Now the mother of only son and suresh's mother is same. That means suresh is the only son of the mother. and the boy in the photograph is suresh's son. That means Suresh is the father of the boy in the photograph.
Explanation: Suresh said that he is the only son of my mother's son. It means that Suresh is the only son of her mother. Then the boy in the photograph is son of Suresh. Therefore Suresh is the father of the boy.