Pointing to a girl in the photograph, Amar said, "Her mother's brother is the only son of my mother's father". How is the girl's mother related to Amar ?
Only son of Amar's mother's father is Amar's maternal uncle.
So, the girl's maternal uncle is Amar's maternal uncle. Thus, the girl must be Amar's sister.
So, the girl's mother is Amar's mother also.
option A.