Below are a narrative description and partial conceptual database model of Tulip Hair Salon's revenue business process. $($Applies to Multiple Questions$)$

$$Tulip Hair Salon provides hair service $($hair cut, hair coloring, styling, etc.$)$ to customers. Customers who want to get hair service from Tulip Hair Salon can schedule appointments for hair service via phone call. During this phone call, a customer should be assigned to a salon staff who will provide service$($s$)$ on appointment date. A customer can reserve one service type or many service type for each scheduled appointment. A receptionist will record the scheduled appointments to the database. If it is necessary, a receptionist will reserve equipment$($s$)$ for a scheduled appointment. For walk$-$in customers, a receptionist should also record the appointment scheduled to track salon staff's availability.

While most of scheduled appointments result in delivery of service to customers $($keeping appointment$),$ some scheduled appointments can be canceled without any service delivered. For each scheduled appointment event, a customer can have only one kept appointment event. If a customer need multiple appointments, a receptionist will initiate new scheduled appointment. No appointment can be kept if there is no record of scheduling appointment event.

When a customer receives the service$($s$)$ scheduled, a salon staff will record the service$($s$)$ delivered and salon staff$($s$)$ who provide service$($s$)$ to a customer. If any equipment was used during the appointment, a salon staff will record this information to track the usage of equipment.

Cash receipt information should be recorded on date the appointment was kept for revenue process. Receptionist will collect cash from the customer and enter information to the system. Each cash receipt event in revenue process can involve only a single customer.

Records for Resources $($or resource type$)$ and Agents should be entered before any events occur.

$$

Which of the following best describes association between Scheduling Appointment and Kept Appointment events in extended REA business process model?

Fulfilment association

Stock Flow association

Duality association

Reservation association