If A $ B means A is brother of B; B * C means B is son of C; C @ D means C is wife of D; A # D means A is son of D.
How is C related to A?
I. Maternal grandmother
II. Maternal aunt
III. Aunt
IV. Mother

Question: 以下哪项是正确的？
Options:
A. 仅 III, B. 仅 II, C. II 或 I, D. 仅 I, E. IV 为真
Answer: E
True statement: IV