Explain the procedures the auditor would use to verify the cost of inventory, assuming the client uses

Question:

Explain the procedures the auditor would use to verify the cost of inventory, assuming the client uses the following valuation approaches:
a. FIFO valuation on a periodic inventory basis
b. LIFO based on an index of FIFO cost computed each year and then used to adjust the inventory to LIFO
c. Average cost on a perpetual inventory basis