Choice "A" is correct. If total inventory is used to apply the cost or net realizable value rule, then total cost and total net realizable value are calculated as follows:

Cost is less than net realizable value, so the inventory will be reported at the cost of $610,000.Choice "b" is incorrect. This answer would be correct if the lower of cost or net realizable value rule was applied to individual inventory items rather than to total inventory.
Choice "d" is incorrect. The net realizable value of $630,000 exceeds the cost of $610,000, so the inventory should be reported at cost.
Choice "c" is incorrect. If total inventory is used to apply the cost or net realizable value rule, then total cost and total net realizable value are calculated as follows:

Cost is less than net realizable value, so the inventory will be reported at the cost of $610,000.