Under which inventory system (periodic or perpetual) and inventory costing method (specific identification, FIFO, LIFO, Average Cost) would cost of goods sold be determined each time goods are sold by using the cost of the most recently purchased goods? Under which inventory system (periodic or perpetual) and inventory costing method (specific identification, FIFO, LIFO, Average Cost) would the only use of cost flow assumptions be to compute ending inventory by looking at first the cost of the most recently purchased goods, then working backwards?