How to show ABC

#include <iostream>
#include <string>

using namespace std;

class a
{
public:
    // Your code starts here

    virtual string m1() { return "A"; }

    //virtual string m1() { return a::showA();; }
    //virtual string showA() { return "A";  }

    // Your code ends here
    virtual string m2() { return "A"; }
    virtual string m3() { return "A"; }
};

class b : public a
{
public:
    virtual string m1() { return "B"; }
    // Your code starts here
    virtual string m2() { return "B"; }
    // Your code ends here
    virtual string m3() { return "B"; }
};

class c : public b
{
public:
    virtual string m1() { return "B"; }
    // Your code starts here
    virtual string m2()
    // Your code ends here
    {
        return b::m2();
    }
    // Your code starts here
    virtual string m3() { return "C"; }
    // Your code ends here
};

int main()
{
    a* a = new c();

    cout << a->m1() << endl; // Should print "A"
    cout << a->m2() << endl; // Should print "B"
    cout << a->m3() << endl; // Should print "C"
}