Midwest Department Stores allows all its employees to purchase goods worth up to $1,000 in retail value each year at a 50% discount. Mark, an employee of Midwest, took full advantage of this policy one year and received a $500 discount. Midwests gross profit percentage on sales to customers is 45%. The normal industry discount was only 30%. How much must Mark include in gross income?

A. $0

B. $50

C. $200

D. $500