The correct answer is: C. Sister
The woman’s mother has only one daughter, who is the mother of the man. This means that the woman and the man are siblings. The woman’s mother is the man’s grandmother.
Option A is incorrect because the woman is not the man’s mother.
Option B is incorrect because the woman is not the man’s daughter.
Option C is correct because the woman is the man’s sister.
Option D is incorrect because the woman is not the man’s grandmother.
Option E is incorrect because the woman is related to the man’s mother.