static void Main(string[] args)
{
Person ps = new Person();
ps.Hello();
Student st = new Student();
st.Hello();
st.SetAge(21);
st.ShowAge();
Teacher tc = new Teacher();
tc.Hello();
tc.SetAge(30);
tc.Explain();
}
static void Main(string[] args)
{
Person person = new Person();
person.Hello();
Student student = new Student();
student.SetAge(21);
student.Hello();
student.ShowAge();
Teacher teacher = new Teacher();
teacher.SetAge(30);
teacher.Hello();
teacher.Explain();
}