For each of the following tax treatments, determine the concept, construct, or doctrine that provides the rationale for the treatment:

a. During the current year, Trafalger Corporation pays $475,000 in estimated tax payments. Trafalger determines that its actual tax liability is $490,000, so it pays only $15,000 with its tax return.

b. The Parsnip Partnership is an accrual basis taxpayer. During 2009, Parsnip deducted as a bad debt expense a $5,000 account receivable that it determined it could not collect. In 2010, Parsnip receives a $1,000 payment on the account. Parsnip must include the $1,000 in its 2010 gross income.

c. Kuri sells land for $30,000; its cost was $20,000. Under the sales agreement, the buyer is to pay Kuri's son $10,000 of the sales price. Kuri must recognize a gain of $10,000 on the sale.

d. Jevon owns 20% of the stock of Cowdery, Inc., an S corporation. During the current year, Cowdery reports income of $45,000 and pays no dividends. Jevon must include $9,000 in gross income.