We have learned that this waiting time model is only valid if the utilization is less than $100\%($this means, on average, there is enough resources to serve all customers$).$ What happens to the waiting time if there is not enough resources to serve all customers?

Select one only:

a$.$ System variability leads to an increase in flow time because inventory builds up in the system and causes queuing.

b$.$ System variability causes inventory to be reduced in the process.

c$.$ System variability allows bottleneck utilization to be greater than $100$ percent.

d$.$ System variability means that customers will never have to wait.