The correct answer is: A. Simple average method.
The simple average method is a method of costing inventory that uses the average cost of all the units of inventory on hand at the beginning of the period plus the cost of all the units purchased during the period, divided by the total number of units on hand at the end of the period.
The weighted average method is a method of costing inventory that uses the average cost of all the units of inventory on hand at the beginning of the period plus the cost of all the units purchased during the period, weighted by the number of units of each type purchased.
The periodical average method is a method of costing inventory that uses the average cost of all the units of inventory on hand at the end of each accounting period.
The periodic simple average method is a method of costing inventory that uses the average cost of all the units of inventory on hand at the end of each accounting period, without taking into account the cost of units purchased during the period.
The simple average method is the simplest method of costing inventory, but it can be inaccurate if there are large fluctuations in the cost of inventory. The weighted average method is more accurate than the simple average method, but it is more complex to calculate. The periodical average method is less accurate than the weighted average method, but it is simpler to calculate. The periodic simple average method is the least accurate method of costing inventory, but it is the simplest to calculate.