For Infinite Source Models,which of the Following Will Equal the Average

Multiple Choice

For infinite source models,which of the following will equal the average time a customer is in the system?
I.Average number in the system divided by the arrival rate
II.Average number in the system multiplied by the arrival rate
III.Average time in line plus average service time

A) I only
B) II only
C) I and III
D) II and III
E) III only