Holiday Travel Vehicles sells new recreational vehicles and travel trailers. When new vehicles arrive at Holiday Travel Vehicles, a new vehicle record is created. Included in the new vehicle record are a vehicle serial number, name, model, year, manufacturer, and base cost. When a customer arrives at Holiday Travel Vehicles, he or she works with a salesperson to negotiate a vehicle purchase. When a purchase has been agreed upon, a sales invoice is completed by the salesperson. The invoice summarizes the purchase, including full customer information, information on the trade-in vehicle (if any), the trade-in allowance, and information on the purchased vehicle. If the customer requests dealer-installed options, they are listed on the invoice as well. Th e invoice also summarizes the final negotiated price, plus any applicable taxes and license fees. The transaction concludes with a customer signature on the sales invoice.   Identify the classes described in the preceding scenario (you should find six). Customers are assigned a customer ID when they make their first purchase from Holiday Travel Vehicles. Name, address, and phone number are recorded for the customer. The tradein vehicle is described by a serial number, make, model, and year. Dealer-installed options are described by an option code, description, and price.   Develop a list of attributes for each class. Each invoice lists just one customer. A person does not become a customer until he or she purchases a vehicle. Over time, a customer may purchase a number of vehicles from Holiday Travel Vehicles. Every invoice must be filled out by only one salesperson. A new salesperson might not have sold any vehicles, but experienced salespeople have probably sold many vehicles. Each invoice only lists one new vehicle. If a new vehicle in inventory has not been sold, there will be no invoice for it. Once the vehicle sells, there will be just one invoice for it. A customer may decide to have no options added to the vehicle or may choose to add many options. An option may be listed on no invoices, or it may be listed on many invoices. A customer may trade in no more than one vehicle on a purchase of a new vehicle. The tradein vehicle may be sold to another customer who later trades it in on another Holiday Travel vehicle.   Based on the preceding business rules in force at Holiday Travel Vehicles, draw a class diagram and document the relationships with the appropriate multiplicities.