[Valmont]

Or we can let Base/Derived manage class A on their own:

#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>

using std::cout;
using std::cin;
using std::endl;
using std::string;
using std::vector;
using std::ostream;

//------------------------------------------------

class A
{
public:
  A(){}
  vector<string>& model_lookupTable()
  {
    return ModelLookupTable_;
  }
private:
  vector<string> ModelLookupTable_;
};

//------------------------------------------------

class Base
{
public:
  Base() : theA(new A)
  {
     theA->model_lookupTable().push_back("Base") ;
  }
  ~Base()
  {
    delete theA;
  }
  //
  virtual void some_function()=0;
  //
  const vector<string>& get_table()
  {
    return theA->model_lookupTable();
  }
protected:
  A* theA;
};

//------------------------------------------------

class Derived : public Base
{
  public:
    Derived(){}
    void some_function()
    {
      theA->model_lookupTable().push_back("Derived");
    }
};

//------------------------------------------------

int main()
{
  //1) Constructor of class Base will create an instance of class A.
  //2) Then it will modify the property of class A as a demo.
  Base* myInstance = new Derived;
  //Constructor of class Derived will modify property of class A. Class A's
  //instance is created by class Base.
  myInstance->some_function();

  //So what do we got for myInstance?
  for(unsigned i =  0; i < myInstance->get_table().size(); ++i)
  {
    cout<<"From instance: "<< myInstance->get_table()[i]<<endl;
  }
  
  delete myInstance;
  //A's instance cease to exist after deletion of myInstance.
  return 0;
}