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