Which of the Following Are the Three Major Components of a Queuing

Which of the following are the three major components of a queuing system?

A) The source population,how customers exit the system and the queuing discipline
B) The number of servers,the service speed and the waiting line
C) The source population,how the customer exits the system and the queue discipline
D) The source population and the way customers arrive at the system,the serving systems and how customers exit the system
E) The service speed,the queue discipline and the waiting line