13. let s and t be two non-empty sets and f : s t be a function such that for all subsets a and b of s, we have f(an b) = f(a) n fb). then (a) there exists an a

13. Let S and T be two non-empty sets and f : S T be a function such that for all subsets A and B of S, we have f(AN B) = f(A) n fB). Then (A) There exists an ACS such that f-(f(A)) # A. (B) There exist disjoint subsets A and B of S such that SA)n f(B)#o. (C) fis injective. (D) None of the above statements is true.