有如下程序：#include using namespace std;class ONE{public :virtual void f(){cout<<"1";}};class TWO : public ONE{public:TWO(){cout<<"2";}};class THREE : public TWO{public :virtual void f(){TWO::f();cout<<"3"; }};int main(){ONE aa,*p;TWO bb;THREE cc;p=&cc;p->f();return 0;}执行上面程序的输出是______。