下面程序输出的结果是【 】。 include <iostream> using namespacc std; class A { public: void show(){tout<<'A!';} }; class B: public A{ public: virtual void show(){cout<<'B!';} }; class C: public B{ public: virtual void show(){cout<<'C!';} }; void show_info(A *i){i->show();} void main(){ A ia;B ib;C ic;show_info(&ia); show_info(&ib);show_info(&ic); }