20. Which of the following should be included in 2016 expense? a. The cost of inventory purchased in 2015. b. The write-down of inventory to net realizable value that occurred in 2015 related to items that are sold in 2015. c. The write-down of inventory to net realizable value that occurred in 2016 related to items that are unsold as of December 31, 2016. d. All of the above