关于一个指针和继承的有关问题，小弟我想问问大家，为什么输出的是这样的

#include<iostream>
using namespace std;

class A
{
    public:virtual void print(void)
        {
            cout<<"A::print()"<<endl;
        };
};

class B:public A
{
    public:virtual void print(void)
        {
            cout<<"B:print()"<<endl;
        };
};

class C:public A
{
    public:void print (void)
        {
            cout<<"C:print()"<<endl;
        };
};

void print(A a)
{
    a.print();
}

int main(void)
{
    A a,*pa,*pb,*pc;
    B b;
    C c;

    pa=&a;
    pb=&b;
    pc=&c;

    a.print();
    b.print();
    c.print();

    pa->print();
    pb->print();
    pc->print();

    print(a);
    print(b);
    print(c);

    return 0;
}