求高手，以下程序运行结果以及具体过程？？？？？？

#include<iostream.h>
class Base1
{
public:
    Base1(){cout<<"class Base1"<<endl;}
};
class Base2
{
public:
    Base2(){cout<<"class Base2"<<endl;}
};
class Level1:public Base2,virtual public Base1
{
public:
    Level1(){cout<<"class Level1"<<endl;}
};
class Level2:public Base2,virtual public Base1
{
public:
    Level2(){cout<<"class Level2"<<endl;}
};
class TopLevel:public Level1,virtual public Level2
{
public:
    TopLevel(){cout<<"class TopLevel"<<endl;}
};
void main()
{
    TopLevel obj;
}