In December of 2019, Bob sold land to Natalie for $80,000. He reported the sale using the installment method. At the time of the sale, the land had an adjusted basis of $20,000. Natalie made a down payment of $25,000 in 2019 and agreed to pay $11,000 per year plus interest for the next 5 years. The payments were to be made May 1 of each year. Before the 2021 payment was made, Bob sold the installment obligation for $30,000. What is Bob's gain (or loss) for 2021 on the sale of the installment obligation? A. $19,000 B. $33,000 C. $11,000 D. $44,000