Bob and Elizabeth, both 55 years old and married, sell their personal residence to Wolfgang in 2011. Wolfgang pays $660,000 and assumes their $90,000 mortgage. To make the sale they pay $20,000 in commissions and $10,000 in legal costs. They have owned and lived in the house for seven years and their tax basis is $200,000. What is the amount of gain recognized (not realized) on the sale?
A. $0
B. $20,000
C. $50,000
D. $520,000