Which of the following is used to make an abstract class?

#include<iostream> 
enum curioustab
{
    a=1, b, c
};
int main()
{
    int x = c;
    int &y = x;
    int &z = x;
    y = b;
    std::cout<< z--;
    return 0; 
}

#include<iostream.h> 
class CuriousTabBase
{
    public:
    int x, y;
    CuriousTabBase(int xx = 0, int yy = 5)
    {
        x = ++xx; 
        y = --yy;
    }
    void Display()
    {
        cout<< --y;
    } 
    ~CuriousTabBase(){} 
};
class CuriousTabDerived : public CuriousTabBase
{
    public:
    void Increment()
    {
        y++;
    }
    void Display()
    {
        cout<< --y;
    } 
}; 
int main()
{
    CuriousTabDerived objCuriousTab;
    objCuriousTab.Increment();
    objCuriousTab.Display();
    return 0; 
}

#include<iostream.h> 
class CuriousTab
{
    int x; 
    public:
    CuriousTab(short ss)
    {
        cout<< "Short" << endl;
    }
    CuriousTab(int xx)
    {
        cout<< "Int" << endl;
    }
    CuriousTab(float ff)
    {
        cout<< "Float" << endl;
    }
    ~CuriousTab() 
    {
        cout<< "Final";
    }
};
int main()
{
    CuriousTab *ptr = new CuriousTab('B');
    return 0; 
}

#include<iostream.h> 
class CuriousTabArray
{
    int Matrix[3][3]; 
    public:
    CuriousTabArray()
    {
        for(int i = 0; i<3; i++)
           for(int j = 0; j < 3; j++) 
              Matrix[j][i] = i + j; 
    }
    void Display(void)
    {
        for(int i = 0; i < 3; i++)
           for(int j = 0; j < 3; j++) 
              cout<< Matrix[j][i] << " "; 
    } 
}; 
int main()
{
    CuriousTabArray objCuriousTab;
    objCuriousTab.Display();
    return 0; 
}