ABC Corporation Awarded John 1,000 Options in 2013; Each Option

ABC Corporation awarded John 1,000 options in 2013; each option allows him to purchase one share of ABC Corporation stock for $20. The ABC stock was selling for $18 per share at the grant date. In 2015, John exercised the options when the stock's selling price was $40 per share. In 2017, John sells the stock for $50 per share. How much gain does John recognize in 2017 when he sells the stock if they are incentive stock options?

A) $0
B) $10,000
C) $20,000
D) $30,000