You arrive at the airport and wonder to what extent the security checkpoint is a lean operation. Among other things, you observe that it takes about 30 seconds to check an ID, scan a passenger for weapons, and X-ray their luggage. However, the average customer spends about 20 minutes in the process. This observation is an example of which of the following? 

a. Waste of capacity 

b. Waste of a flow unit’s time 

c. Waste of materials 

d. This observation is unrelated to lean.