Which of the class definitions below is a subclass correctly defined according to its definition stated here?

Which of the class definitions below is a subclass correctly defined according to its definition stated here?

class k $\{...\}$;

class f: public: g$,$ h $\{...\}$;

class c: public d$,$ e $\{...\}$;

class a: public b $\{...\}$;