下面程序输出的结果是【 】。 include <iostream> using namespace std; class A { public: virtual void show() {cout<<'A!'; }; class B: public A { public: void show() {cout << 'B!';} }; class C: public B{ public: 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); }