单选题

下面代码的输出结果是什么 ( )

Question

下面代码的输出结果是什么 (      )

#include <iostream>
using namespace std
class A
{   
    public: void virtual f() 
    {       
        cout << "A" << " "
    }
}
class B : public A
{   
    public: void virtual f()
    {       
        cout << "B" << " "
    }
}
int main(){
    A *pa = new A()
    pa->f()
    B *pb=(B *)pa
    pb->f()    
    delete pa, pb
    pa=new B()
    pa->f()
    pb=(B *)pa
    pb->f()
    return 0
}

A. A A B A

B. A B B A

C. A A B B

D. A A A B