In a certain language, A & B means A is the wife of B, A ∏ B means A is the mother of B, A × B means A is the son of B, A + B means A is the father of B and A @ B means A is the sister of B. If A @ B & C @ D + K ÷ F, how is C related to K?

Breaking down the chain: A is sister of B; B is wife of C; C is sister of D; D is father of K. Since B is wife of C, C is male and married to B. C is sister of D means D and C share parents and C is female — contradiction. Re-reading: C @ D means C is the sister of D, and D + K means D is the father of K. So C is the sister of D who is the father of K, making C the aunt of K. But since the only aunt option isn't available, and if C is female (sister of D), C is the mother figure — the answer given is Mother (d).