Why is base-class destructor called on derived object when destructor of derived class is non-virtual?

Question

Why are all destructors, ~D(),~C(),~B(),~A() being called in the example below?

There is only one virtual destructor: that of A.

Here is the code:

#include<iostream>
using namespace std;

class A
{
public:
  virtual ~A()
  {
    cout<<"destruct A\n";
  }

};
class B:public A
{
public:
  ~B()
  {
  cout<<"destruct B\n"; 
  }
};
class C:public B
{
public:
  ~C()
  {
    cout<<"destruct C\n";
  }
};
class D:public C
{
public:
   ~D()
   {
     cout<<"destruct D\n"; 
   }
};

int main()
{
    A* ptr = new D();
    delete ptr;
    return 0;
}

Answer 1

Once A's destructor is declared virtual, the destructors of all derived classes are also virtual, even if they aren't explicitly declared as such.. So the behaviour you see is exactly what is expected