问为什么从基本类型转换到派生类型会提供这样的功能？

EN

  class Person {

    public:

    Person()
    {
        cout << "Creating Person Class" << endl;
    }

    void about_me()
    {
        cout << "I am a person" << endl;
    }
};

class Student : protected Person {
    public:
    Student()
    {
        cout << "Creating Student Class" << endl;
    }

    void about_me()
    {
        cout << " I am a student " << endl;
    }

};

int main()
{
    Person* pperson = new Person();
    Student* pstudent = new Student();

    pperson->about_me();
    pstudent->about_me();

    pperson-> about_me();

    ((Student*)pperson)-> about_me(); // this is the line where I do the cast

    return 0;

}

  Creating Person Class
Creating Person Class
Creating Student Class
I am a person
 I am a student 
I am a person
 I am a student