Inaccesible due to its Protection level? Help me please

I need help figuring this out, what am I doing wrong my book doesn't give a clear explanation on how to deal with this and neither does the online help in VS2008.

Can you show me how to do this correctly?

Another error I am getting:

Cannot Create an instance of the abstract class or interface "Person.Person"

Member Person.Person.rnd' cannot be accessed with an instance reference; qualify it with a type name instead

Person.cs

  public abstract class Person
  {
        private string title;
        private string firstName;
        private string lastName;
        private string address;
        private string 开发者_如何学Gogender;
        private string dateOfBirth;
        private string userID;
        static Random rnd = new Random();
        // constructors
        public Person()
        {

        }//end default constructor

        public Person(string aTitle, string aFirstName, string aLastName,
                      string aAddress, string aGender, string aDateOfBirth)
        {
            title = aTitle;
            firstName = aFirstName;
            lastName = aLastName;
            address = aAddress;
            gender = aGender;
            dateOfBirth = aDateOfBirth;
        }
  }

Student.cs

 public class Student: Person
 {
        public override string GenerateUserID()
        {
            this.userID = firstName.Substring(0, 1) + lastName.Substring(0, 5);
            //ERROR HAPPENS HERE
            this.userID = this.userID + this.rnd.Next(1000, 9999);
        }//end method Generate UserID
 }   

PersonTest.cs

static void Main(string[] args)
{
    //ERROR HAPPENS HERE TOO Cannot Create an instance of the abstract class or interface "Person.Person"
    Person testPerson = new Person("Mr.", "Merry ", "Lanes", 
                                   " 493 Bluebane RD", "Male", " 8-06-1953 ");
}

private fields and properties cannot be accessed by subclasses. If you use protected, you should be fine.

You can't create a Person object since it's abstract.
If you are not a native english speaker or if you just don't know what abstract means, grab a dictionary and see what this word means.
In the OOP world it means that you can only instancate classes that derive that class.
For further reference google polymorphism.

This means that your code should be:

static void Main(string[] args) 
{ 
   Person testPerson = new Student("Mr.", "Merry ", "Lanes", " 493 Bluebane RD", "Male", " 8-06-1953 ");
}

You should also change your Student constructor to accept those parameters and move them up to the base class like this:

public Student(string aTitle, string aFirstName, string aLastName, string aAddress,    
        string aGender, string aDateOfBirth)
: base(aTitle, aFirstName, aLastName, aAddress,    
        aGender, aDateOfBirth)
{
}

And as others have mentioned, if you want to access a member variable of the base class from a derived class use protected.
protected means this is public for my derived classes, private for anyone else. Also, your rnd variable is static and private.
This means you can't access it from this because it belongs to all Person objects and not to specific instances. You can remove this or if you think you need to, remove the static. Make it protected as well.
Good luck.

In Student.cs, you're using userID and other members that are private in the base class, make it protected and it'll be running. More information, Access Modifiers (C# Programming Guide).

The next exception is thrown because you're instantiating an object of Person which is an abstract class. Abstract classes are just meant to be inherited, therefore if you wish to create an object of that class, remove the abstract modifier.

firstName and userID are private in the base class, so the subclass cannot access them. Change them to protected.

In your Student class, you're trying to access userID, which is a private member of the Person class. If you want to be able to access base class members from a derived class, you need to mark them protected.

private means that only the class itself can access it, i.e. no sub-classes. Therefore your Student class can't access userID.