Based on the concept of service blueprinting, what is the "line of visibility? " select one: a. the architectural line drawn on the the blueprint, below which are notes not meant to be seen by the client. b. a metaphoric divide between the preparation work required before a service is to be provided, and when the actual service begins. c. a metaphoric divide between the parts of a service that a guest sees and what they do not see. d. a physical wall that literally prevents guests/customers from seeing what back stage employees do.