For each of the following accounting practices, state the most appropriate accounting concept or principle underlying the practice: 1. After a payment has been disbursed to a supplier, the accounts payable clerk is required to file documents relevant to the payment made. This ensures that transactions recorded are supported by proper source documents. 2. Kelsey Co. writes down its stocks of finished goods to estimated selling price when the selling price of the goods fall below cost. 3. Playstore Co. sells a plant to plant to Toystore Co. and immediately leases it back for the remaining life of the asset. Playstore Co. still records the asset in its accounts. 4. At Waldo Co. office equipment that have a life more than one year but which cost less than $1,000 is written off as expense on the date of its initial recognition. However, all other office equipment is capitalized and depreciated over their economic lives.