26. Consider the following sequence of operations for disjoint sets (there is no set initially): Make-Set('a'), Make-Set('b'), Make-Set('c'), Union('b','c'), Make-Set('d'), Make-Set('e'), Make-Set('f'), Union('e','f'), Union('a','b'), Union('a','f')

Which of the following statement(s) is(are) true after this sequence of operations?