Answer:
d. a Poisson probability distribution.
Step-by-step explanation:
Based on the information provided within the question it can be said that the best description of the arrival pattern is provided by a Poisson probability distribution. This concept that tries to map out the probability that a given number of the same event occurred during a fixed interval of time. Which in this case would be the other arrivals during the set amount of time you are in the waiting line.