写出下列程序代码运行的结果【 】。 include<iostream.h> class A{ public: virtual void disp() {cout<<' calss A!' <<(end1;} }: class B: public A{ public: void disp() {cout<<' class B! ' <<end1:} }; class C: public A{ public: void disp() {cout<<'class C! ' (<end1;} }; void main() { A a, *ptr; B b; C c; a. disp(); b. disp(); c. disp(); ptr=&b; ptr->disp(); ptr=&c; ptr->disp(): }