In queuing theory, the nature of the waiting situation can be studied and analysed mathematically if_________________?

A. complete details’of items in, waiting line are known
B. arrival and waiting times are known and can be grouped to form a waiting line model
C. all variables and constants are known and form a linear equation
D. the laws governing arrivals, service times, and the order in which the arriving units are taken into source are known
E. all of the above