Which of the following statements is/are true? a. Under the periodic inventory system, cost of goods sold and inventory on hand are continuously updated as inventory is bought and sold. b. When debiting Purchases and crediting Cash under the periodic inventory system, a purchase of inventory on account must have been made. c. Cost of Goods Available for Sale - Ending Inventory = Gross Profit. d. Under the perpetual inventory system, cost of goods sold and inventory on hand are continuously updated as inventory is bought and sold