下面程序的结果是多少？怎么分析的 谢谢！！！！

class Base{

public:

       int m_a;

       Base(int a = 2):m_a(a){printf("A %d",m_a);}

       virtual ~Base() {printf("B %d",m_a);}

};

class Derived : public Base {

public:

       Derived (int a = 4):Base(a){printf("C %d",m_a);}

       ~Derived (){printf("D %d",m_a);}

};

int main()

{

      Base *aa,bb;

      aa =new Derived;

      delete aa;

      return 0;

}

//记住：构造是先从父类开始构造，再到子类，析构以相反的方向析构！

#include <cstdio>

Base *aa, bb;

aa = new Derived;

delete aa;