To determine how C is related to A, we need to analyze the given familial relationships one by one:
- A is the mother of B.
- B is the husband of D, which makes D the daughter-in-law of A.
- D is the daughter-in-law of E and has no siblings.
- F is the brother of one of the parents of C. Since C is the son of D, F is either the brother of D or B. Given that D has no siblings, F must be the brother of B.
- C is the son of D.
From these statements, we can deduce:
- A is the grandmother of C because A is B's mother and C is B's son (D's son).
- Thus, C is the grandson of A.
Therefore, the correct answer is:
Grandson