Urban's Barbershop has two barbers available to cut customer's hair. Both barbers provide roughly the same experience and skill, but one is just a little bit slower than the other. The process flow below shows that all customers go through steps A and B and then can be served at either of the two barbers at step C. The process ends for all customers at step D. The numbers in parentheses indicate the minutes it takes that activity to process a customer. Which step is the bottleneck for this process