Let the alphabet C be $\{$a$,$ b$,$ c$\}.$ Let the language X be the set of all strings over C with at

least two occurrences of b$.$ Let Y be the language of all strings over C that never have two

occurrences of c in a row. Let Z be the language of all strings over C in which every c is

followed by an a$.($Recall that any string with no c$$s is thus in Z$.)$