单选题 有如下程序:#include<iostream>using namespace std;class GA{public: virtual int f(){return 1;}};class GB:public GA{public: virtual int f(){return 2;}};void show(GA g){cout<<g.f();}void display(GA &g){cout<<g.f();}int main(){ GA a;show(a);display(a); GB b;show(b);display(b); return 0;}运行时的输出结果是( )