Im learning C#. There is a question in a book (Exam Ref 70-483) which makes little sence to me, because I can't find any examples of it anywhere. I understand it in terms of eliminating the wrong answers and the right answer must be there. 

1. You have a private method in your class and you want to make invocation of the method possible by certain callers. What do you do?

A. Make the method public.

B. Use an event so outside users can be notified when the method is executed.

C. Use a method that returns a delegate to authorized callers.

D. Declare the private method as a lambda.

Correct answer 'C': "The method can see whether the caller is authorized and then return a delegate to the private method that can be invoked at will."

What is an example of this? What do they mean by authorized caller? There is no mention of authorized caller in the book. The only thing I could find about delegate and method authorization was about WCF and authorization, but that is for sure out of scope here. Well. I hope someone could shed some light on this! There are so many tough questions like this... well if not tough questions, difficult to understand answers.