Inventory Sales Employees Customers 0..- Cash Cash Receipts Refer to the association marked with the number 5 in the preceding diagram. Which of the following is the best example of a business rule that constrains the association? a. Sales are allowed if they include at least one inventory item. b. Sales are prohibited if they include more than one inventory item. c. Sales must include at least one inventory item. d. Sales are allowed with the manager's approval in advance. e. None of these are the best example of a business rule