Polymorphism

[omerd]

Hello.
I have 3 classes. B and C inherit from A. I want that class B will be able to call functions of C, so I tried to do this:

class A
{
    public:
       A(int b=0) {a=b;}
    protected:
       void Print() {cout<<"Hello world"<<endl;}
    private:
       int a;
};
class B: public A
{
    public:
       B(int b=0): A(b){}
       void Do(A& a) {a.Print();} //error
};
class C: public A
{
    C(int b=0): A(b){}

    int c;
};

but i get an error:
error: `virtual void A::Print()' is protected.

How can I do it without using "friend" (and without making Print public) ?