c++多态性问题求解决

补充函数头部跟下面的完整句子，希望会的帅哥美女帮帮忙，感谢帮忙！

class member
{
    public:
        member() {}
        virtual void answer() {cout<<"I am a member"<<endl;}
};
class teacher : public member
{
     public:
        teacher() {}
        void answer() {cout<<"I am a teacher"<<endl;}
};
int main()
{
    member *who;
    member mem;
    teacher tch;
    who = &mem;
    who->answer();
    who = &tch;
    who->answer();
    
    return 0;
}